In the previous post, I posted pictures of my homemade hangboard mount/Blank Slate imitation.  Here are the schematics for the board:

1. Iron Gym Pull-up Bar (like this one): $30 retail - can be found for $15-20.  I bought mine for $15 from clearance at Target. 
2. 3/4 inch x 2 feet x 4 feet of plywood.  I bought this for $24 at Home Depot, although I'm sure there are cheaper sources.  Which reminds me -- the height of the hangboard is actually an even 2 feet to account for the plywood dimensions.  I just shaved half an inch from the top and half an inch from the bottom.
3. Wood glue/4 large bolts/4 large nuts: ~$10.  EDIT: 8 nuts/bolts, sorry!

The mount was pretty easy to make.  The "face" is pretty self-explanatory: just cut to dimensions and round the corners.  The back section that connects to the pull-up bar was made by gluing two layers of plywood together to make a 1 1/2 inch block and then cut to size.  To connect the back section to the face, I embedded 2 nuts into the back block (before gluing the two layers of plywood together) then used 2 flat head bolts (3/8 inch, 16 thread count) to fasten. I think gluing the back would work, too, if you didn't want an easily removable back.  If you're going to glue the back, make sure it's bomber because the glue will essentially be supporting the entire rig.