That link is exactly what I was looking for.
After working on this price guide page I am now thinking Ecart is the answer, without a checkout. I was originally thinking that the current dropdowns did determine the subsequent dropdown menus, but they do seem to be independent.
If I add an updatable cart and give each option in the dropdowns a value as a product option, I think this might mimic the current menu.
Problem is, after years of using ecart, I have never figured out how to add product options...