Which clutch and flywheel do I need?

After seeing the prices on new flywheels.....I'm ok with a good used one. Is it ok to buy a decent used one or would I run into vibration problems? If I could keep from spending $300+ I'd be happy. I'm already shelling out a few grand over the next month or so finishing up my engine build and getting it in the car, any money I could save would be great!