There is always eBay and Amazon. Those two and other websites dealing with auctions are where I'd go, though there are other online stores (I think) selling such things. The bad part is that the online stores are usually selling them used now, since the PSOne is about 11 years old now...
I don't think EBGames does anymore...Although, a PSOne/PlayStation1 has satisfied me, and you don't sound like a big gamer...Though, I'm sure you wouldn't spend 600 on a PS3, as even Schwartzenegger thinks that's too much.