Manuscript proofreader

I have completed my first book and would now like it proofread before sending the full manuscript to a publishers. The manuscript is approx 90 A4 pages and is made up of 11 short stories linked by a running narrative. I have sent sample chapters to various publishers already and have received (so far) two requests for the full manuscript - exciting. While I understand this is no guarantee of publication, my chances of getting published will greatly improve if the manuscript is polished.
Please could you tell me how much this will cost either by hour or a full cost for the job.
Thank you Gill