From my experience, the best proofreading is to do it manually as all the best software proofreaders cannot locate all the errors. Even if a manuscript were proofread manually, there is still a possibility of errors. Hence the best way is to read it carefully and see if there are errors in the manuscript.
My bid is tentative since you did not indicate how many pages the manuscript contains.
I charge US$ 0.50 per page for proofreading. I hope this is reasonable enough. For a 500 page manuscript, that should be $ 250. If it is 550 pages, we could haggle to $ 250.
I have CDs here on medical terminology. I could check the work based on the medical terminology that is contained in the CDs.