I have been doing IT systems analysis for over 30 years. I'm now retired, but I enjoy the work and am interested in freelancing as a "hobby" to allow me to continue doing the technical writing, documentation, and related functions that I enjoy. I've used VISIO for many years, having gotten my first copy years before Micorsoft bought them, , and am proficient with the tool. I'd enjoy recreating your manual as electronic pages with VISIO. Given the sample, I'm estimating that the 50 pages can be recreated as VISIO pages in about 75 to 100 hours. The variance depends on the amount of text that will need to be fit inside the various objects on the pages, etc., and the amount to tweaking needed to polish the pages to a professional level. I can deliver the completed pages as VISIO files, or as .pdf files if that works better for you.
It is possible that my estimate of the hours is high, but I'd rather estimate high, and finish under estimate than find out that the work was more complex than I thought, and go over the initial estimate.
Regards,
David Fuller