Bought car 3/12 and 11/12 heater and AC control.

Bought car 3/12 and 11/12 heater and ac control shut down and also some other electrical malfunctions[ delay of windows an lights operating]. I took the car to local allpurpose repair place[ goodyear] who said they could ck the electical for $95. They recommended a new heat - ac main control for $900 plus labor. I got it on line used for $120 and put it in myself. Still doesnt work. So I took it to a small foreign care repair bussiness ive used before. He quoted me $900 for an electronic part[ moduole]. Now he wants $1100 more for aother module thats shorted out. Is this a case of not diagnosing the original problem correctly. How flexible in pricing should I be. Im a self imployed home improvement contractor for 30 years and try to up- front with my customers if it will hard to diagnose. The mechanic works out of his garage and probably has limited diagnostic equipment.