At Valley Forge, the Continental Army struggled to get through the cold winter weather. Warm clothes seem to be an extremely cheap item to obtain.
Why did the Continental Army struggle so much just to get shoes and clothes? Were they more expensive back in the time period? Was there a shortage? If so, what caused the shortage?
It's hard to believe difficulty they had of obtaining clothes/shoes to keep warm, especially from a modern perspective, where these things are easily able to be purchased for a cheap price.
To add a bit to what DarthNetflix says, you are correct in expecting that today clothes and shoes are inexpensive, compared to their cost in the pre-industrial world: then they were made by hand, from materials made by hand, transported from maker to seller with more manual labor. Although there would be some variance, of course, happily the State of New Hampshire tried to control prices and wages during the War and you can see some of their numbers here. Their list gives a rough idea of what would be thought reasonable wages and prices of the time. A pair of good half-boots would be 13 shillings, whereas the wages of a carpenter ( usually someone who worked up heavy timber frames of houses, from logs) was 4 shillings a day. So, a pair of boots would be a bit more than 3 days' wages for a common skilled workman. Figured at today's equivalent wages, those boots would be more than $ 300.
One of the skills Washington had gained during his early years in the French and Indian War was the ability to keep an army together despite little support from the government . The following year when the Continental Army overwintered in Morristown NJ, they were far better prepared, and though there was grumbling about rations there was not the acute suffering of Valley Forge.
Morristown is now a US National Historical Park and well worth a visit, by the way.
Samuel Flint et.al., New Hampshire. Report of Commissioners on bureau of labor statistics, to the Legislature, June session, 1872.
Money, dear boy!
The Continental Army and the Continental Congress had no money and a nearly worthless currency. They operated on credit, but they hadn't had much time to build any financial credibility (this continued to be a problem well after the Treaty of Paris in 1783). Congress needed the individual states to supply the funds for the war, but they were often more interested in funding their own defense. They were highly suspicious of any centralize authority, including the Continental Army. John Adams and George Washington would frequently complain of this perceived selfishness in the face of national crisis.
Most American merchants didn't want to operate on credit and only accepted cash, so they withheld their wares from the cash-poor government. The army caught a big break when the French funds started rolling in, but before that it was running on what amounted to IOUs.