Why is it an issue? I reckon a purchase would end up WAAAAYYY cheaper than a rent. You said you've got 1000s to do. That's NO
post-meridional peripatation. Think along the lines...
1000s x say 2000dpi x 16bit depth x slow USB2 links = a heckovalong time - heaps of PP...

1 way or an1ther, I read that you'll need to get a scanner of the order of a 2ple of 100 dollars. Don't get the useless jpeg-only cheapery for <=$100