Mufflers for my Kohler 25 is $140. What are others doing that need to replace a Kohler muffler. It seems that there should be some sort of fabrication. Perhaps a muffler shop? Has anyone fabricated with motorcycle parts?
If the ends where it bols to the block are good a muffler shop (if they can get the pipe...kinda small for a car) can fabericate it for you (provided you can provide the replacement mufflet to fit the pipe...moped muffler or the kolher one that has 2 slip joints could work well (it's about 30 bucks).
Or try a search on ebay using kolher muffler as the key word, it will bring up a few with links to online stores (olot of them) are MUCH (about half) cheeper than buying from a small engine shop.