[Note: the answer below uses the old British pre-decimal system of pounds, shillings and pence (usually expressed £-s-d). There were 12 pence to the shilling and 20 shillings to the pound. It's worth noting that according to the Bank of England's historical inflation calculator, £1 in 1914 was worth around £105 today.]

This is a surprisingly complex question, not only because of the number of different combatants involved in the war, and because basic rates of pay were fairly meaningless within a system that also offered numerous and often very generous allowances based on rank, posting and branch, but also because of the tremendous changes wrought by the conflict itself. So as time is short I am going to restrict myself to answering for the British Army only, and only for 1914.

One obvious further problem, from the perspective of this question, is that the professional British army that started the war was officered by men who were rooted in pre-war social mores; a huge proportion of officers did not join the armed forces for the pay, but because they offered a socially acceptable way for high-born men (often younger sons of old and wealthy families) to spend their time. There were, obviously, many exceptions, but on the whole officers serving in 1914 fully expected to heavily subsidise their official pay from their private resources. The most remarkable consequence of all this was that British Army pay scales actually remained essentially unaltered between 1806 and 1914! It took the transition from this model to that of a "democratic" new army, comprised of numerous new regiments raised and officered by men from much less elevated social stations, to at least partially dismantle this system.

In 1914, basic pay in the British Army was therefore low by the standards of the time. Officers were expected to be gentlemen and were generally expected to have the private means of gentlemen. Officers, especially those in the most exclusive regiments, required private means in order to pay for their own uniforms (several different and often elaborate ones were required), additional equipment and mess fees, plus "civilian clothes made by a suitably expensive tailor, and two riding horses." All in all, these costs were so substantial that "a newly arrived second lieutenant joining a cavalry regiment was expected to have a private income at least greater than his commanding officer's annual salary." In practice, every junior officer in a regular British regiment required a subsidy of at least £100 from his family in order to serve with honour.

Those who lacked such wealth were forced to settle for less costly careers in colonial regiments or the Indian Army. The career of Field Marshal Sir William Robertson, the Chief of the Imperial General Staff during the Great War, and the only man ever to rise through the ranks of the British army from private to field marshal, is a good example of the practical implications of low pay. Robertson began his career as an officer by accepting a posting to India where, because the Indian government offered cash awards to men who qualified as interpreters – a set rate for each language spoken – he used his spare time to acquire proficiency in six local languages, from Persian to Gurkhali, in order to supplement his pay. Lack of a private income plagued Robertson's entire army career; "as a junior officer he drank water in the mess while his fellow officers quaffed champagne, and he would leave the room to smoke his pipe - only cigars were permitted in the mess - as pipe tobacco was all he could afford."

Raugh sums up the situation in the late Victorian era as follows: "In 1850, it was observed that British Army officers were 'the worst-paid and hardest-working of public servants.' This trend changed little prior to World War I." Indeed Roberston, who chaired an Army Council committee on pay in 1918, reported that "most officers were receiving much the same pay as 50 or more years ago" while "the cost of living had gone up by 100 percent." The committee recommended significant increases in married allowances, rations, travel expenses and lodging fees, as well as the reduction of the number of items required for full uniform.

OK, so on to the specifics of your question. In the British Army of 1914, the commander in chief was paid at an inclusive rate (excepting field and travelling pay) of £4,500 per year. A general received £800 per year.

However, looking at some specific examples from the top end of the scale may help us to understand the ways in which basic pay was actually a relatively meaningless concept for the most senior officers. As early as 1916, the CinC, Haig, was manipulating the system and contemplating the long term rewards of his service in terms that he thought unremarkable but which would be considered unacceptable today. Notes de Groot:

The fact that his men slept in muddy holes was no reason for Haig to decline a soft bed in a luxurious château. Grouse, salmon, fine wines and the best brandy were sent to him by rich friends at home. Nor did he perceive anything wrong with sending whole lambs and butter from the army stores to his wife so that she would not have to endure food shortages. Luxuries were the confirmation of high authority. In the same sense, extravagant rewards were perfectly justifiable after the war. Already in 1916, Haig assured his wife that 'a grateful nation will not allow me to have a smaller income than I am receiving now! So we will be well enough off to make ourselves comfortable.' Few objections were raised about the luxuries Haig enjoyed during the war, or the rewards he received after it. These were the accepted standards of his class and rank. Greater restraint would have seemed peculiar.

Now, to contextualise:

Cavalry lieutenant colonels received a basic pay of £1 9s and 6d a day, a sum that would be boosted by various allowances. Cavalry majors received 17s and captains 13s 6d. In the infantry, the equivalent rates were £1 8s, 16s and 12s 6d.

The situation at the bottom end of the scale was as follows: at the lowest pay grades, British army privates, second class, received a mere 8 shillings and ninepence a week in 1914, plus food that the army calculated was worth an additional 5s a week. This was a very low wage for the time, but matters could be improved in various ways. Most obviously, there were considerable allowances available for men who qualified in various specialisms – machine gunners received a basic daily pay of 2s 6d (17s 6d a week) in 1916. Even more importantly, there were generous marriage and separation allowances – 7s a week for separation and an additional 18s a week for a soldier supporting a wife and two children. Overall, a married private with two kids would receive £1 11s 9d a week – about par with the wages of a coal miner, but still less than half the contemporary wage of a police constable, which were 72s a week. The steadiness of the job – men signed on for engagements of several years at a time, in an era when few civilian jobs offered anything like such job security – was generally held to offset the relative paucity of the wage.

Sources

Royal Warrant for the Appointment, Promotion and Non-Effective Pay of the Army 1899

Stephen Badsey, Doctrine and Reform in the British Cavalry 1880–1918

Alexander Greenwood (ed), Field-Marshal Auchinleck: A Biography of Field-Marshal Sir Claude Auchinleck

Gerard de Groot, Blighty

Gary Mean, The Good Soldier: The Biography of Douglas Haig

Harold Raugh, The Victorians at War, 1815-1914: An Encyclopedia of British Military History

William Robertson, From Private to Field Marshal

David Sibley, The British Working Class and Enthusiasm for War, 1914-1916