I wouldn't see why not, just set the table saw blade at an angle when you cut out that rabbet along the bottom edge. Making it adjustable on the other hand.....
As far as the price goes... if you had to buy the hardwood, magnets, and handles, (not any of it left over from other projects) you would be in it for at least half of that price I would imagine. But if you're someone who would appreciate this jig, I would bet that all of the materials would be laying around the shop already. He would probably make more on a downloadable template for 10 bucks, no overhead, and many would spring for $10 for an "instant" product.
M2C
Jason