A regular riding horse, of average age in eighteenth century England would have cost approximately 4 pounds, we know from probate inventories. Average income for labourers (the lowest-paid workers) was about 12 pounds a year, we know from the accounts of building firms employing labourers. So, a horse was about a third of the wages of the lowest-paid workers. Transported to today, with a minimum wage of about 15,000 pounds, that would translate to 5,000 pounds. Now, whilst that sounds cheap, labourers could not afford a horse because (a) they needed those 12 pounds virtually entirely to feed their families (so were much worse off even than minimum-wage earners today) and (b) horses require a lot of food themselves, which makes them very expensive in the upkeep (a horse needs either several acres of good-quality grassland, or the equivalent in fodder). But for the 'middling sorts', which might enjoy annual incomes of 50 to 200 pounds a year (so much more than they would spend on food, even when eating more and more expensively than a labourer, leaving them quite a bit of income to spend on 'luxuries'), and who might even own a few acres of grassland and some stables, a riding horse was eminently affordable, probably just as affordable as a car today. Source: am an historian of the long eighteenth century.