Yeah, in many ways a 944 checks a lot of boxes - cheap, reasonably plentiful and would probably be more or less competitive with no mods (just gut it, put a cage in, etc.). "Cost to maintain" would be a lot worse than many cars, but I still think a 944 would be high on my list. Either that or an E30/E36 for many of the same reasons.
Do to the large amount of prize money available in Chump
, I think 90% of it is to build/run something you like and just have fun.