Electrical floor heating kits run US$10 to $15 per square foot, but bulk wire only costs $2.50. With the controller, you're still running under $4 a square foot. I have a construction background, but not electrical. Are there any good books out there that takes a novice through the steps of buying just the parts and making one's own?
Just don't. This is clearly the best answer.
If you really want to cheap out perhaps you could buy a complete kit with just one square foot mat, analyze the wire used, and try to source a designated radiant wire of similar dimension and resistance. Then fold and spindle that in a similar way to the mat squares.
Remember your fire insurance likely excludes work done in flagrant violation of the building codes. Use of regular copper wire, while possible, is just not advised.