As far as the initial dollars invested, my guess is the ZX6R or F3 is your best bet.
I raced a 97 GSX-R600 for the last two years, and I'll tell ya, if you're seriously looking to LEARN to ride, this is not it! But if you do succeed on a GSX-R600, you will be able to ride just about anything.
There's something to be said about RPM management!
But for lay down and repairs, I say the GSX-R is your best bet, since there are still a lot of 97+ GSX-R600's on the race circuit and many many parts to be had.