If your looking into the Audi, look into GIAC or APR, very high line reliable companies that run on the conservative side. The internals on the 1.8T audi are good for 350hp Daily Driver on 93 octane after that your playing with fire.

cost would be 3500-4000 front mount intercooler included with PCM tuning as well.

2004 Audi A4 1.8T Quattro 6spd \ GIAC FXKO3 Software \ AudiTT 225hp 386cc Long Neck Injectors \ Valentine One HArdwired \ S4 Lip Spoiler, 18" HP Evo on 245/45/18's \ Bailey's Diverter Valve \ Stasis Streetsport Coilovers \ APR Full Exhaust.