air compressor size????

Something to think about is that with a quality compressor you can get parts for the pump. With a bargain one you replace the pump as a whole. It all comes down to how much volume, psi you need and how long you plan on keeping it. As with most things in life you get what you pay for.

Another thing to think about is your power supply. 110, 220 single phase, three phase. Depending on your power supply you might only be able to go so big.

I wouldn't be afraid to buy another used quality compressor.