I have replaced most of the parts on my 91-300E with the 103 engine. The only item I have not replaced was the dist cap. The price sound about right, you may find the high price item such as the O2 sensor or the belt tensionor to be cheaper. Even at the dealership, the repair department charges 15% above list. I don't think a good repair shop will let you bring in parts for repair.
The main problem I see here is, they did not get you approval, and you are down $1500.00.
Take it back, Do something that you have control, call your bank to put a stop payment on your check. The worst case is the shop not release your car.
Good luck, jack