I found a pretty reputable place that charges $65 to install, PER amp, wiring included. That's pretty reasonable but for 2 amps that's a whopping $130.
So I was wondering: what if I pay them only to install the 2-channel amp, and then I can install the mono sub amp myself?
As I understand it, the first amp is much harder because the wires need to go to the battery and the front speakers, but the mono amp just gets plugged into a distributor box and then straight into the sub.
$130 is pocket change. Pay the pro to do the work. You need to run RCA lines as well, and set amp gains, run speaker wiring, etc. Not just a matter of running power from the distro block.
ask them for a deal on the install since you're doing both amps at once time. See if you can get them down to $110 or $100