Last winter, after considering building my own dredge, I bought a used 3" for about 1/4 the cost of a new one. It has metal parts and I don't believe I could have built it for the cost I gave for it. Considering the cost for an engine and pump, etc, I'd recommend searching for a used one.
With gold getting back down close to $700 and a lot of new dredgers out there who bought a new dredge this past spring realizing that they are not going to get rich prospecting, you can find a lot of great deals right now. Probably even more deals over the next several months. Just take a look on eBay! There are more and more dredges on there and many are going pretty much on the "cheap!"
Not that a homemade one can't be done - I don't think anyone here is saying that it can't be done - I think folks are just recommending to go with a system that has already been engineered to work rather than spending lots of time on hit or miss testing. If I built a homemade dredge, I think I would be running lots of tests to see how much color I am losing out the end of the sluice. In fact, I have done this with my "commercial" dredge that I feel like I "stole"!
At any rate, pissin' matches on this forum don't really help anyone determine what might be best for them to do.
Much gold to you all - homemade or not!
Lookin