By far the best single din head unit ever made is Pioneers DEX-P99rs. There has never been another unit that even specs close to it in terms of sound quality and processing.
Pioneer USA - DEX-P99RS - Reference Series CD Tuner with Digital DSP and USB Port with Digital Direct Signal Transmission
For speakers I'd run Dynaudios Esotar line ( E650, Mw142, and E110 tweet) they are sexy
Subwoofer would be a Dynaudio E1200 subwoofer in a carbon fiber enclosure since Ive been itching to build one.
Amplification would be a trio of JL HD amps, mainly because of their small size and the amazing technology built in ( HD600/4 on tweets and midrange, HD600/4 bridged on midwoofers,HD750/1 on subwoofer)
So about 5 grand for equipment and doing it myself Id spend another 1500 on wiring and install material. It could all be stealth and nobody would expect the monster of a setup hidden in the panels.