Those bellows aren't that expensive; I bought a few spare OMC Cobra ones (Volvo and Cobra used to use the same exact bellows) for 60-80 bucks IIRC.
Now if you have to get into other things like the gimble bearing, or ujoints the price can REALLY go up, not so much due to parts but labor time
I have done this job myself, (bellows only) as long as the drive and pivot housing come off easily, then it's not a hard job, I can get it done in 2 hrs taking my time and checking everything else along the way.....