The motor and tranny mounts are a few hours job as long as you don't strip any allen bolts. If you have two jack stands, a floor jack, and a block of wood you can do it. It will cost you $50 in parts for two Lemforder or Phoenix brand mounts (only buy those).
Here is a guide on motor mounts:
Motor Mount Replacement Guide
The transmission mount is a similar job, instead of lifting the engine you lift the transmission by its pan. A few bolts and it's swapped. You can probably get by with a Febi brand mount.
The door locks may be an easy fix...see this diagnosis guide. You can probably get them fixed yourself for under $100 including the price of a vacuum pump/gauge.
Vacuum Door Lock Diagnosis Guide
Send the cruise control amp to JamesDean on this forum (look him up and PM him for details). He can fix it for under $100.
If you can get the stuck door open, and the door panel off (see guide below) you can then replace the check strap. It's just a few bolts. You can use a front door style check strap, they are available on here aftermarket for under $20.
Door Panel Removal Guide
The transmission shift bushings are cheap but a pain to replace with a special tool. Search google for W123 shift bushing special tool to find solutions. Again you can do this for under $50 probably including the tool.
If you want to get more of your money back, fix the above, pull the greasecar setup and sell it separately, and then you can sell the wagon for more since it will have a much smaller list of issues.