I've found that those intercoolers on Ebay, usually named "medium intercooler", are good. around 2psi pressure drop across it and good thermal efficiency doesn't drop off until 300 bhp.
Re: Bigger Intercooler on a budget
[Re: sebasteeno]
#1597230 24/03/201708:5024/03/201708:50
Try to get an intercooler with at least a cross section of 76mm thick/250mm tall (300mm would be perfect!)or 90mm thick /200mm tall. Inlet and outlet pipe should be with inside diameter of 57mm (external diameter 63-70mm). Below those dimensions you will have some unwanted lag even with stock turbo.