I have built 2 so far, and one of them is the underfolder that you are describing. I bought a Polish kit from Shooters for $159 plus shipping, which included all parts except for the receiver. The barrel was pressed off the trunion, and all rivets were removed. I went with the Arsenal 1.6mm receiver, type 2 for $69.99. Unless you are a FFL dealer, you will probably pay an additional fee for their handling of paperwork. Is it easy to build one? I guess that depends on several factors, such as your proficiency with hand tools, what kind of tools/equipment you have, and to an extent, the condition of the parts kit you purchase. Some kits require removing parts of the old receiver, and others like mine came completely disassembled. You can buy the receiver (from Global Trades) with either the front or rear trunion installed, or both installed, for an additional fee. You can go to www.globaltrades.com to view receiver options. Having built AR's also, I can say that AK's will require more work and hand tools. Most of the work (in my opinion) involves assembling the trunions to the the receiver. Pressing the barrel in is easy if you have the right set up. The underfolder rear trunion will require additional holes in the receiver for the folding stock hardware, if you install this part yourself. If you like building AR's and FAL's then you should enjoy building an AK. Yeah, you could send your parts kit to Arsenal and they will build you a gun, but that takes away from the fun of building it yourself...