Below is the recently completed gun prop "Black Betty" also known as the "Rock Gun". It's a mean looking, massive, double barrel shotgun pistol prop that can be cocked and reloaded, has working triggers and interchangable bullets. For all the construction details and a lot more images, take a squiz at the blog.
Material costs: AUD$200 (most of which was in the cost of paint treatments).
Project proposals/requests can be emailed to this
(For more things I've built have a look at: Hobby Projects).