There's this spot called High End Car Stereos here in Philadelphia.
They charged me about $680 for the install, but that install included running wires/cables for 2 amps, and installing 1 4-channel amp. (second amp was on its way)
The job took about 3-4 hours each time (did a install first where it stuck out about an inch, had them re-do it next day to make as flush as possible, but could've been done in 3-4 hours on the first try, if you show them an image of mine). The price jumps up a bit more, another $100, if you want to use the factory steering wheel controls.