oh lord....im going to try to point you in the right direction, b/c theres a good chance the rest of the posts following mine will be you getting flamed
sounds like a kenne bell? are you serious?
i didnt deal too much with the 03/04's as i owned a sn95 cobra, but i believe 99-04 mustangs can be fitted w/ the 03/04 fascias...
try svtperformance.com for both your visual and s/c needs
depending on what you get, ie a v6 or gt the prices for s/c will vary...
personally if i were you id keep my eyes peeled for an sn95 cobra (94-98, preferably the 97-98 yr models, as they have the 4.6 dohc motor instead of the 5.0) s/c w/ a nice tune and call it a day....i picked up my 97 2 years ago w/ 46k miles for $7500 there was a s/c gt on here for sale a while back for 8kl i think, you just have to keep your eyes peeled, deals are everywhere