RPC I costs about 120€ with a little luck (150€ without), Supplement I about 20€, Supplement II (which is of little use if you don't own the original books, like most supplements) is free and has always been free. Supplement II is the second supplement to
RPC I and the first supplement for
RPC II.
I own only
RPC I, but for the time it covers it is absolutely essential.