I have a 2002 Windstar

You don't want to pay for a proper diagnosis, but you're willing to spend a lot more for a computer that is likely not needed? The Check Engine light is turned on by the Engine Computer when it detects a problem that could adversely affect emissions. There will be a diagnostic fault code stored in it. That code will not say to replace parts. It only indicates the circuit or system that needs further diagnosis.

The other problems are related to the Body Computer. I'd start by looking at the door ajar switch which might be built into the latch assembly

The reason for the outrageous diagnostic cost is the equipment is very expensive. Go out and buy a scanner for yourself, then see how you feel when someone wants to borrow it. You're luckier than most people if you have someone willing to borrow you theirs. When you're done with it, take them a box of cookies, ... Preferably chocolate chip!