Oil-tanned leather technically doesn't exist, but it's the term that people use for leather that's finished a particular way. There's definitely oil involved, but the oil has nothing to do with tanning.
If you were barefoot outside, your feet will only get as hot or as cold as the ambient temperature. If you're wearing socks and shoes, they will either let excess heat escape (if your feet heat up) or they'll let cold air in due to the materials of your socks and your shoes.
It isn't always the case with any consumer goods that you have to pay top dollar or else you'll be miserable...but it's usually the case that investing in quality can get you better results in the long run.
So let's talk about what "a good price for leather boots" actually is.