I've been wanting to get another AK to play with, but the cheaper the better.  I've thought about picking up a lo-cap WASR and opening up the mag-well so it'll accept hi-cap mags.  I'm not sure of the legalities of doing so, however.

Anyone have any insight on how legal this would be, or where I could go to check it?  

Century has been doing it for years. Nothing illegal about it. Just make sure you have the proper US parts count.

Also have to be careful. Some (but not all) of the Romy low-caps actually have a low-capacity front trunion, which will require substantial modification or outright replacement in order to function with High-capacity mags. But it is worth it: I bought a low-cap Maadi for $200 and converted it. I worked slowly, and opening the mag well took about 1hr. If I were to do it again, it would probably only take about 20-30 mins with a Dremel. Then you need your 5/6 compliance parts and you are ready to rock and roll.