I highly recommend the Fujitsu fi-6130. (There are probably newer models now) It is compact (5" by 10.5" footprint), connects by USB, has a bullet-proof document feeder, and is blazingly fast, scanning both sides of a sheet of paper simultaneously, at a rate of 30 pages (60 images) per minute at 300dpi resolution. (resolutions up to 1200dpi are available and slower.) I used a fi-6120 (one model earlier than mine) to scan 176,512 images (probably about 120,000 individual pages) of medical records over a period of several months, and other than installing a maintenance kit to replace worn feed rollers, it was 100% trouble-free.

It is probably less than optimal for photographs (it's OK, but SWMBO's Epson flatbed does a better job with color fidelity and saturation) but for document scanning it's hard to beat.

The downside is that it cannot do flatbed scanning (document feeder only) and it is just a bit over your $300 budget. Like, $500-$600 over. I paid $869 for mine, and have never regretted it for an instant.

tanstaafl.