These scanning systems are all combinations of hardware and software. Since the real thing you are buying here is convenience and less effort on the part of the scanner, you want it all in one place. You certainly don't want to have to build any features yourself. Though many of these scanners do have bar code processing in them so a sheet of bar code stickers might well work.

The digital camera approach is interesting, but harder than it seems. The resolution is sufficient, and it's fast and in colour, but you need to get the page completely flat for a good quality scan, and lit in a way that doesn't have glare. One approach is to put glass or plexi over the page, but that's work and glare can be a problem -- you need a dark room or a nice arrangement of lights.

A more interesting approach I thought of would be to make a suction table, sort of like an air hockey table in reverse, with lots of small holes in a flat surface, and a mild suction that is keyed to your shooting process -- ie. it goes off and on in a smooth way perhaps with a foot pedal or automatic controls to make it easy to slap down pages.

I considered that having $10/hour teens with cameras might be an effective method, in that they should be able to do a page every few seconds easily. For the best quality you want the camera dead on, which means mounted above the shooting area, but for the highest speed, bringing the camera to the documents (hand-held) might be sufficient.

It's possible that cheap workers in India with digital cameras could beat the price of the automatic scanner. Doing duplex with cameras takes twice as much scanning though.