I work as a mechanic at an outdoor power equipment sales/service business. Unfortunately most starters for briggs, kohler, etc are $100 or more (sometimes waaay more). If just the bottom commutator case is broken, it may be available separately from the magnets / amature / bendix and cost well less.
What is the brand, model, and spec/serial number of the engine? I can look it up and find what your options are. The I.D. numbers should be on a plate/sticker somewhere on the engine shrouding or stamped into the flywheel shroud.