Custom mounts for what? The problem with the CRX IMO is it still needs a drivetrain, so by the time you're done you could be out another few hundred at least since IME Honda stuff is $$$. It's as nutty as VW diesel crap. I think you'd be better off looking for complete vehicles if you're gonna go bat****crazy on it, provided of course you thoroughly research your gearing options, since by aero'ing it up, reference area isn't as much as of a concern. In fact, as Basjoos shows, once ya get past the weight/aero issues, gearing will still hold ya down unless ya don't mind going 70+mph.
I'd go for one of these, or whatever is similar in yer area. A small, cheap, complete, 4cyl.
http://capecod.craigslist.org/car/636481599.html
http://capecod.craigslist.org/car/637680297.html
http://westernmass.craigslist.org/car/629776242.html
http://westernmass.craigslist.org/car/649532400.html