If you are interested in a full commercial version of this (sharing an analog whiteboard with a link), check out http://smartkapp.com
(Disclosure: Am employee of said company)
(Disclosure: Am employee of said company)
It definitely sucks to prototype something that already exists, but it's probably a good lesson too.
Also, another person in this thread mentioned a 42" one from China thats $120 [1]. That is more in the "cheap" range.