Those labor quotes are pretty cheap, but then again, it's Circuit City.
Don't waste your time with a 10 ga amp kit. That's really puny.
All of that Sony stuff is garbage, including your head unit.
$733 won't get you anything jaw-dropping, but you can take your time and get a lot better stuff out there.
There has to be several shops in the DC area. Go somewhere that specializes in car audio. In fact, go to several. Some of them will be worse than CC, so just feel it out and do some research.
Good luck!