GPUs are no longer used for Bitcoin mining. The recent GPU shortage is caused by the raise of thousands of little altcoins. It's obviously unsustainable, and it's going to end in a big crash, and all these GPUs will flood the market. It's hard to predict when it's going to happen (I'm guessing this year), but if you're patient you will be able to buy GPUs very cheaply.
I wouldn't consider Ethereum to be "a little altcoin". While there may be a correction in the market, I don't think it will be "bitcoin vs. everything else"; at this point it would probably be all cryptocurrencies, or something more specific (individual coins, or classes, but probably not "scrypt-based coins as a class")
