Believe it or not, Pages in the iWork package may be just what you are looking for.
It depends on how complex you want the formatting to be. If you live near an Apple store, you could go try Pages on a computer there and see if you can find a Pages knowledgable sales droid.
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.