While this thread is active, I just wanted to post links to two other camera related threads for people that want the information. They cover a lot of settings related topics, but would be useful in selecting cameras as well. Daniel had posted these in another thread and I thought they would be useful here:
http://diybookscanner.org/forum/viewtopic.php?f=1&t=65http://diybookscanner.org/forum/viewtopic.php?f=1&t=75Specifically related to this thread, one of the important bits from those threads is that the some of the A series powershots have real apertures as opposed to the SD series powershots that likely just use a ND filter to block out light to mimic a smaller aperture. Here is the post that as of that time listed the camera with real aperture settings:
http://diybookscanner.org/forum/viewtop ... &t=75#p767Also of note is that the SD series cameras don't have an input jack for AC power, they require a type of battery compartment adapter, which are quite a bit more expensive even on ebay. I think that's true across the board for the SD series.
Overall then if you're searching Ebay or Craigslist for cameras, the A series seems to be better if you find one with a resolution that seems appropriate. As Daniel mentioned in the first post in this thread, look for SDM/CHDK compatibility first of course. I've found Craigslist is a pretty good source for camera listings lately. I've seen an A590 listed for $125 and several A series for less.