I would bet you could find a "readability" editor on any college campus for 20$/hr.
They would find all the misspellings, incorrect word choices, and corrupted sentences etc, pretty quckly.
For good research structure, that's a kind of wrote formatting, taught in MA studies of English literature or Writing.

My kid is a Legislation Editor down at our state capital, she bill's out at about 75$/hr.

I bet you could clean up enough in one visit to make a book easier to use as a reference. Indices, biblio, etc.

Out there doing it best I can.