I think that with little luck you might find decent razors under 10 bucks from flea markets, but you have to recognize what is a decent razor and what is not, or is the condition of the razor worth trying to make it a good shaver.

Forget eBay for now. Straight shaving seems to become quite popular, and currently people are paying brainless amount of money for some razor brands.
I would recommend you to watch classifieds where you can still find shave ready razors with reasonable price.