Without recasting, are these correct? Are the hyphens correctly placed in all?
•a $5-million- to $10-million-a-year enterprise
(or: a $5- to $10-million-a-year enterprise) - Hopefully, the reader won't construe '$5' as 'five dollars'. I think I like the succinctness of this variation, do you?
•a $100-million-a-year industry (good with three hyphens?)
As an NES, but not an English teacher:
I would avoid, wherever possible, repeating myself.
In such a case, I would use "per" or "/" rather than multiple hyphens.