Textbooks do not cost $800 if you buy them used through half.com and then resell them.
8.01 is the normal version of physics. It's kind of like the first half of AP Physics C. 8.012 is the version with more math and more proofs. If two classes have the same number they're the same class; they might have been taught in different years.
For USAPHO you probably want to try and find lots and lots of practice problems on the Internet, after you're done with 8.01 (and maybe 8.02 as well, if they also include that material). Good luck.