The Grinder-In-A-Box:

Above is a picture of a grinder built by a knifemaker from a kit available on the web: the EERF, or Grinder in a box.  I really think this is a screaming deal- you get all of the steel parts to build the frame and platen or rotary platen for this grinder, sans wheels, fasteners, and motor, for $250 U.S. plus shipping.  And dig this, the whole package fits into a Priority Mail Flat Rate box- $10.20 anywhere in the U.S..  Many have built it, adding to the range of options for modification, and the instructions on the website as well as on Bladeforums are good and thorough.  Here's a link to the site:
For those of you who really like to start from scratch, and have even less money, I have posted a link one level up (in the main Grinders page) to CAD plans for cutting the frame and platens out which can be downloaded for free.