Hi adrenaline
I routinely buy out of print ebooks and send them for scanning. Based on my own experience:
1. No scanning service can convert a pdf into a decent epub/mobi. There are too many OCR errors in scanning to even consider this, so save the $10.
2. A pdf scan of 1200 dpi for an ebook is overkill and just produces a monstrously large file that will choke most programs.
3. I buy the books to read, so my workflow is to convert the pdf to html in Abbyy Finereader and then to convert the html to epub using Sigil. I have a pretty good idea of what to look for now, so the whole process is not that tedious and time consuming. My accuracy rate is about 95%, which is sufficient for me since I do the conversion for my own use only (I'd rather spend the time reading instead of comparing every single character).
If you only need the ebooks to search text, would not a simple scan to pdf with OCR work? Why would you need to further convert them to epub/mobi?