I have been through this a few times, and have designed a lot of scanning rigs over the past few years.
If you want great quality on a budget, the best option as far as dynamic range, low noise and good framerates @ 2K is the Point Grey Blackfly BFLY-U3-23S6C-C.
You can easily get 30fps via USB3, at full bit depth. The camera is easily triggered using a $2 hall effect sensor and magnet, the camera itself is tiny and is easily retrofitted onto an existing projector or edit table.
The manual trigger and high framerate allow you to capture in realtime.
You can use an enlarger lens and cheap extension tubes to give a razor sharp image across the entire frame. The lens is typically under $100. I have used these in Super8, 16mm and 35mm scanners with great success, the results have often won shootouts against the Spirit 2K and other scanners.
As for DSLRs, you can often use a HDMI capture board, such as those from BMD and capture the stills from the computer that way, but the blackfly is very good value and gives astoundingly good results.