Can you take a 5 gallon cornelius keg, cut out 2/5 of the center, and weld it back together to make a 3 gallon keg (or smaller)? The 3 gallon kegs are much more expensive ($70 vs. $20) and harder to find.
Yuri_Rage did it, and I recall him saying that he would NEVER do it again! I don't know anything about welding, but apparently the stainless in the kegs is very thin and he had a heck of a time. It might have been about two years or go that he posted about it- a search might turn it up.