Custom components:
A pair of Vifa Tweets (D26NC-05-06) - $60/pair (or around $35 on Ebay).
A pair of Vifa 7" mids (M18WN-19-04) - $100/pair.
Link to Vifa's at Speaker City There are also some really nice 7" Vifa mids here:
PE Link for $70/pair.
Then a pair of passive crossovers (I like this
a/d/s set) - $20.
Based on my experience with these Vifa tweets (I've got three pair of 'em) and Vifa mids (I've got the 5" mids), I'd say they'd sound markedly better than the Infinity or Alpine components at roughly half the cost. The tweets are very smooth and detailed with excellent dispersion charasterics. My 5" mids have a very warm mid-range with surprising mid-bass abilities (I can only think the 7" models to have even better mid-bass). I'd just make sure to pick a crossover with a tweeter level adjustment to help fine-tune to your liking.
Just some thoughts...