Two days ago I saved literally $600 from the dealer costs, just by purchasing the 3 wires on my own (the dealership gave me the parts) and installing it myself. My car is out of warranty.

For those interested here's a breakdown of dealer costs and what I paid in parenthesis. The parts I bought are the same parts as the Original Equipment Manufacturer (OEM) parts (the ones the dealer would use), except that they aren't branded with the car maker's name.

The wires were the negative battery cable, which has a chip in it that performs power management to the battery.

• battery cable w/ chip: $279.35 ($150.75)
• some kind of cable adapter, just a wire with a special plug on it: $29.26 ($16.44)
• another adapter of some kind, again wires with special plug: $86.54 ($24.27)

Total for parts: $395.15 ($191.46 incl. shipping). I was quoted $800 as parts and labor.

So right there I saved $200, and installing it took an hour, 40 minutes of which I spent googling things before I finally discovered that one wire coming off the adapter is only used to transport the car when it's new and left unconnected afterwards.