I built one out of a 30 gallon plastic barrel I paid $5. for. Bought the featherplate 1/2 inch plastic off
ebay for $25. Fingers off
ebay for about .55 cents each. found a motor for $35. and additional parts for about $30. I have about $175. plus labor in mine, (bought enough fingers for a 50 gallon barrel, didn't use them all) but need to add wheels and handles to mine as it sets on concrete blocks at the moment. I used a motor off a floor buffer, and mounted the featherplate off the output of the buffer drive, that is designed to run at 175 rmp. Seems to work ok so far. I don't know that I would recommend that for someone doing lots of chickens, but works for us, as we raise 50 in the spring, and 50 in the fall, and will process 10-20 birds at a time.
Buy the book, well worth it. If you are not mechanically inclined, stick to the directions to the tee. Most anyone that can run a saw and a drill can build one according to the plans. If you are a scrounger, and enjoy working with things mechanical, then make it work with what you can find. The featherplate and fingers will be the most expensive purchases for a scrounger.
You just can't beat naked chickens in 30 seconds flat at the push of the button. Now if we could just speed up the gutting part of the process.