Fees are based on the complexity of the subject matter, length of text, density of material, and allotted time. I typically charge a per page rate for all indexable pages i.e., any page I have to read or look at for indexable material. Rush jobs (less than 2 weeks) increase the cost. The range is typically from $4 to $10 per page.
For new clients I request one half of the fee in advance, with the balance due upon receipt of the invoice. For established clients I will allow full payment upon completion. For very large books, or books that come in sections and may take a long time to complete, I do progress invoicing. Arrangements can be made on a project-by-project basis.
I use a dedicated indexing program called wIndex and deliver the completed index as a Word document. I use The Chicago Manual of Style rules but can alternatively follow your house style as a basis for the indexes produced.