The difference is the cheap ones are cheap and you shouldn't put them on your car. The best one I'd recommend is the Process West. It's not cheap, but it's what you need/want. The only other option I'd consider is getting a used STI intercooler if you want to save yourself $600. It's not going to cool nearly as well as the PW unit, but it'll still definitely be an upgrade over your current one, and it's not a bad match for a VF30 turbo since that's not that big of a turbo.