Just to start playing, all you need is that versions PHB. If you're going to DM a campaign, however, you'll also want the MM and the DMG.
Getting 3.0 or 3.5 books at this poing is nigh impossible, unless you can find someone selling them used on Amazon. However, IMHO if you're looking at that style of play I would highly recommend Pathfinder. 4.0 books are currently still available, but will be hard to find once 5e (or whatever they're going to call it) comes out.
3.5 books can often be found used at bookstores; that's how I got mine, and they were in wonderful condition. Pathfinder is very similar to 3.5, although it's also more expensive (I believe the core rulebook costs over $70).
I guess it depends on where you live. I have not seen any 3.5 PHBs in the bookstores. The Pathfinder core rulebook is only $33 on Amazon (http://amzn.com/1601251505).
The other problem with 3.5 is that it is no longer maintained. Pathfinder is essentially D&D 3.75, and has a team of people working on it.
3.5 for life! ive retained my players, DMs, MM 1 & 2, and epic handbook :D but browsing e-bay ive seen large quantities of 3.0 and 3.5 handbooks for sale before
If I were to start a 3.0, 3.5 or 4.0 game, what books would I need?