in order to reprap to be widely used more important than cheapness and ease of construction is its usefulness, that is the designs you can download and print. for example paintball guns, fun things but expensive. you could probably build one out of mostly(screws nuts springs are needed and maybe metal barrel) rp parts. also it might be profitable to make and sell them. at the moment my darwin is far from fully functional so on my part the thought is on hold, if i ever get around to this idea again i'll look up the design and make it happen