Plus you say you want to have them done, so you don't have to edit each one. Sorry, but you will still need to do color correction and fine tuning on just about every photo, if you want them to be good. So you might as well do three at a time and crop each one out and save them.
Even if you had some automated scanner that had a sheet feed, and every photo is identical, which they are not, you are going to want to make them the best you can, which means editing each individual photo.
By the time you get done scanning photos for hours and hours, you are going to have to edit each one. That means you buy the scanner, take at least six hours to just scan the photos, that's three at a time, then figure at least another six hours to crop and edit them all.
You might re-consider dropping them off at some shop and having it done on professional equipment, which whatever you or I can afford will not be as good as what the pro equipment will do.
If you have some photos that you are worried about other people seeing, take them in and scan them yourself, then have the rest done by some place that does this for a business. You'll be much happier with the results.
I think you are looking for an inexpensive, fast and easy answer, and there is none if you want to do it right.