I'm working on one now based on one that I found at
Homebrew Adventures. Finding stainless washers has proved to be nearly impossible, so I'm going to buy the bulkhead fitting from AHS (
Link).
I didn't build the fly sparging part on top, so you'd need another $5 in fittings/pipe, but here is what mine cost.
10ft CPVC- $2.29
CPVC to Female NPT - $0.67
1/2" Full port brass ball valve - $5.97
1/2" Male NPT to Barb - $3.88
10 pack of 1/2" CPVC Tees - $1.60
5 1/2" CPVC 90deg Elbows - $1.00
Total: $15.41 + $15.99 for the bulkhead fitting ($31.40 overall)
If it wasn't for that bulkhead fitting, this would be a really inexpensive project. I got fed up with driving to different places only to find out that they don't carry stainless steel washers (after they told me that they did on the phone). I'm going to add the bulkhead fitting in with another order, so the marginal cost for shipping is $0.
Of course I already had a cooler.
CPVC is listed for use with potable water, and it's cheaper and easier to work with than copper. I also went with brass valves for better isolation. I don't care about leakage on the inside of the cooler, but I want to be able to really tighten things down on the outside.
Here's a link to the pictures (so far):
http://www.flickr.com/photos/jragg/sets/72157605748305524/