Take it from someone that is a diyer and knows. To get the a/c and the cc working you will burn through between $600 and $900. I purchased a '85 300D project car for $1500 and have spent the following on just the two items you mentioned.
a) New AC Delco compressor $200 - check this out for your model though because I doubt if yours is the AC Delco unit.
b) a/c pushbutton unit - check it out at partsshop.com - I believe between $200 and $300.
c) Cruise control module - rebuilt - I believe it was around $260.
d) Figure another $100 to the tech that does my a/c work when he evacuated and charged it a couple times. First time was to troubleshoot and second time was to get it to condition it is in now. Unfortunately, I am going to replace the expansion valve over the next few days and will have to go through the evacuate/vacuum/charge sequence one more time so figure another $50 or $60.
The list goes on for new parts but the car runs great and will cruise down the interstate between 75 and 80 mph all day long. Thanks to the excellent old Chassis/Body service manual (purchased off of Ebay), mercedesshop.com and some emails to friends on here I have done everything myself except press in the lower ball joints and vacuum/charge the a/c.
It is my understanding too that you can sink alot of $$ into the self leveling suspensions on the 300TD real fast.