As one of the few Westy owners who has swapped out the AC by myself:
If you have very deep pockets you can probably find a professional who will install a new AC for you with decent quality. The problem with this job is
1) it involves electrical, roofing, and carpentry skills, and also working with fiber glass. That doesn't fall into the common categories for home improvement contractors. You will probably look at hiring an RV repair pro. Those are in very high demand.
2) It is fairly tedious to do right. It took me about 3 weeks working maybe 5h a day. Granted I work slowly and often sit there pondering what the best solution is before I go ahead. Then also you have to wait for glue, paint, or fiber glass to dry. Then there are trips to the hardware store, to get more fiber glass etc. Also I spent a lot of timer researching online what the right wire sizes are, the best fiber glass, and searching the sprinter forum back and forth. It just all adds up.
My wild guess is that a pro would charge you anywhere between $5-$10k for labor only. Then the question is what quality they will deliver for that price. Will it leak? Will the roof start bending under the weight because they skimped on supports? I just didn't want to take my chances with it.
If you search this forum you will find reports of several AC replacement projects. If you take it on yourself I can assure you you'll get good responses on this forum if you post your problems. I'll certainly be responding to your questions.