If you're mechanically oriented and are a good welder, or know someone who is, you can build you own offset bbq smoker. It's common to see offset smokers made from propane tanks.
Here are some links to websites that can help get you started in the right direction:
Where to put the axle
Offset Smoker Build
BBQ Smoker Plans
Here's a picture of the end result as built by Rob Bagby aka "Rub" of Swamp Boys BBQ.