SCSI scanners with Mac drivers are also dirt cheap, and you can get quite high end models for next to nothing.

You can also find SE/30 PDS cards for ethernet and external monitors, which will give you colour video and more screen real estate if and when you need it. Just FYI, the SE/30 and IIsi PDS slots are identical, but no other PDS cards will work.

Search these forums for SE/30 PDS and you'll see what's available.