If you are using MacOS 9.2, there is nothing better than FrameMaker 7. Even though Adobe is scheduled to end support of the Mac version next month, it is still listed for sale on the Adobe website. The the updaters are still available for download. You don't really need support because it just works. OTOH, it is a bit more expensive than your $100 budget.
Several people have suggested that you use a TeX-based solution. There are a few TeX implementations for MacOS 9. OzTeX is shareware and has been around longer than Joan Collins. You can find it here.