I went through this almost 3 years ago when trying to find the latest 2nd car (the GT6 is the primary). The 2nd car is always the mule, to haul GT6 parts and things to big to put in the GT6.
After a lot of research, looking at price, serviceablility, mpg, etc., I came up with the 1995 - 1999 Dodge/Plymouth Neon, specifically looking for one with a manual transmission, no sunroof & no power windows or anything else.
After I got it, I began liking it more & more. It turns out the 1995 - 1999 Neon has an awesome showroom stock SCCA history, believably, because it's fun to drive. I expected only a mule, but it is extremely fun to drive & too much fun on interstate ramps and hilly, twisty, 2-lane roads.
I like it more & more the longer I have it. This weekend, I had to drive some stuff to New Orleans (it's unfortunate that it's the cargo vehicle), usually 1 1/4 tank trip something like a 12 or 14 gallon tank. I realized I'd left my cards and DL at home & had only a 1/2 a tank & a $20 bill in my pocket. So I resolved to drive at 55 mph economy to see if I could make it and if neccessary gas up and turn around if it looked like it wouldn't. I had installed the Mopar Performance engine controller from Dodge which is optimized to sportier response but is supposed to yield lower fuel economy, but at 55 mph granny speed the trip took only 1/4 of a tank each way! I thought the gas gauge was broken! I really really like this car, and I am a picky, critical SOB about cars.
105k mile timing belt interval, excellent rear passenger space, strong enthusiast community for support. Low mileage examples often show up. I would recommend it to anyone, but I think for most folks I'd recommend the 4-door rather than the 2-door version for greatest and most comfortable use.
They made them in various sport/trim levels which includes suspension equipment, but basically the manuals have better fuel economy and fun-to-drive than the autos. The Mopar Performance controllers are available for all of them.
Mine is a 1999 Neon R/T like this one:
I haven't run across anything more reasonable and fun to drive. Cargo area is big, but I put a trailer hitch on it for when I may want to take an engine to a machine shop on a small trailer or something.