I use a wiimote and infrared pen and the whole thing cost less than $100 (using the projector I already had and speakers I already had)

projecting onto regulary whiteboard

I know that didn't answer your question lol but in our school only 5th grade and media center have promethean boards

so I had to make my own - and so far I haven't found anything I need to do that I can't do with my setup and would need a "real" iwb for