Well, I won't call it the best system out there, but to kick things off for the thread, I did:
Sony CDX-R3300 $119.99 + $18 s/h
2 pairs Polk EX-357 $37.99/pr + $12 s/h
From National Audio Center on ebay.
Wiring harnesses from CC $36.06
I still need
DIN tool $5
Soldering iron + solder + wire + ??
So for roughly $275 + some tools I think that I'll make out OK.
If I could spend some more I'd consider
budget component set group buy at ~ $85/pr incl shipping
Any capable HU @ roughly $150 delivered
Infinity basslink @ $230 delivered
4 channel amp? $150?
$700 or so for a pretty decent system.
About the only thing I'd upgrade after that is the subwoofer to a more customized solution, and/or a more powerful amp and/or a satellite capable HU. Hopefully still under $1K.
It always amazes me that the OEM Bose audio systems are > $1K options on automobiles