I can see where A and C is coming from but there is a reasonable price and been taken to the cleaners. A lot of avionics companies take people to the cleaners.
I have always had my work done by David Jones at Airpspeed and his price has always been very good and the quality superb. Not only that he does include all the extra detail you mention in the price. I had my 496 connected to a CB and to the Garmin GMA340A for the sum of £250.
I have also had work done by IAE at Cranfield and found the job to be well done and with a bit of haggling well priced. My AP and HSI were done by IAE and they were 2/3 of the price of another equally reputable company.
Proof that you can get quality and a FAIR price.