Whatever you do, don't buy walmart, or basically any shitty paint. I only really used to work with lexan bodies, so I only know if you wanted to paint like, a lexan windshield or something.
I can't stress enough on using a high quality paint though, and don't skimp on it. Walmart paint just sucks. If you know temps will get hot, get a brake caliper-type paint...one that has high temps before it starts to bubble and such.
What would actually be best is to use a dye rather than a paint though. Dying vinyl interiors tends to work out a lot better. But, if you're stuck on painting, use like a rustoleum, or a flexible type paint so no cracks or chips happen. Your interior shrinks and expands depending on the temperature (ie, rattles more in the winter). Expect prices for the vinyl paint (at auto stores should carry them) to reach around $5/can.
If you want to do a design in it for some odd reason, or to do multiple colors on a single piece, use a nice vinyl masking. Parma/PSE (google.com) makes the best vinyl masking tape you can get at any hobby shop (R/C, slot cars, etc).
I'm really into the actual painting part of it. Painting is almost my specialty since I used to do tons of r/c car bodies, which required a lot more precision. Hell, I even have an airbrush and compressor for it. For the actual painting, everyone should know this but little follow it: use thin layers. Hell, wtf, I'll just be there when you do it lol. IM me on AIM when you want to so I can just meet up with you. I want to take my interior apart anyways.