I was able to find a replacement driveshaft and final drive for a few hundred bucks. The splines were way better than my old ones. The process to change over is not hard, if you have basic tools.
However, its absolutely the case that paying someone to fix an old K will impoverish you unless you’re either already there, of so far from it that you wouldn’t be buying such a bike in the first place.
Which brings me to a question, probably best asked elsewhere: why are K’s so inexpensive to buy, for what (to my mind at least) is such a terrific machine?
Price so cheap: bike is ugly with its failings, they are dated. Stupid design flaws, like you cant use your side stand without creating a cloud of burnt oil smoke when you restart. A semi sealed drive shaft that is guaranteed to fail in about 30-40K miles with no means to lubricate without disassembly......