OK here we go..........
First what do you like?? You are going to get to know this car very well, so you better like it.
Any faveret brands?? Ford, Chevy, Moparetc
How much do you know about cars? WAY to $$$$ to pay others to do your mods
Will it be your only driver? Tough call here. REAL hard to Mod the car that has to get you to school/work.
Now the meat.... You ask for afforbale. See thats a tough one. I am a Ford guy, so I will give you some Ford examples.
A Mustang.........OK the car itself will cost you a lot more to get. BUT parts are cheap, and avalable EVERYWERE. Easyest to restore would be a 65-66, but for a little les money, and a better driving car, I would look to a 67-70
OK here is a od ball for you.. A Maverick. You can probably pick one up for almost nothing, and under the skin it is almost the excact same car as a first gen Mustang. Not as sexy, but cheap.
Almost in the same vain is an old Falcon. same type of car, just older.
Want big? The old Farlanes are a nice size, and can fit a big block motor. IMHO no GM model eaven comes CLOSE to the look of the 66-67 Farlanes. SWEET!!!
Or how about a full size car? The Galaxies/LTD's are an awsome cruzing car. I have a 72 LTD convertible that will pretty much fit any motor I could want under the hood. V10? no problem. 6-71 deisl? No problem.
Now other brands also have a few good choices. Cost wise, you will probably have to dig deep in the models to find a nice one. ie you maybe cant swing a Camaro, but a nova is the same car under the skin.
So give a little more info on your wants. Maybe I can fill in the holes for you. Oh, and one more thing....... Build the car for YOU. Don;t get a brand/model just becouse your frends have one, build the car YOU want. Be diferent.