they jacked the price up cause u brought your own parts. Normally, they provide the wires, which they purchase for pennies on the dollar since they buy in bulk. The bill actually reflects higher cost for the parts and lower cost on labor, so the labor fee doesnt look so bad.
If you bring your own parts, they still need to make their money, so they jack up the labor cost (at least you see what they're really making) and theres also no warranty (well maybe labor) since YOu provided the parts.
It's called "markup" and popular in all of business. Everybody has markup - the auto technician who charges $200 for a part and $125 labor, probably purchased the part for $5... thats $320 for his labor. The reason for this is simple. If he provided an estimate to the customer that says its a $5 part and $320 labor, the guy would never authorize the repair. Fortunately for mechanic, most people are oblivious when it comes to mechanics and they can legally work this. This happens EVERYWHERE.
Short business lesson for you guys that don't know.