I can't attest to this personally, having only used the non-saving version, but I'm seriously considering buying one of these.
http://www.improvelectronics.com/boogie-board-LCD-writing-tablet/boogie-board-rip-LCD-writing-tablet.html
granted, you can't load textbooks onto it or anything, but that makes it a fair bit cheaper compared to buying a full-blown tablet.
the non-saving one was quite good just for scribbling rough working and had a really nice feel.