Engine swap on a 93 Ford Probe GT?

I've been looking at a 93 Probe GT for $500 around my area but the engine has a knock, a BAD knock. I could just rebuild the engine but I really don't want to take it apart to find out that it might need a new crank so are there any engines that are popular swaps on these cars and the cheapest site to find them on? I'd even be alright with a slightly used or rebuilt stock engine. Links appreciated, thanks.