You could use an old refrigerator. I recently found an old one from the 1940's that I got for free. It is porcelain on the inside and after removing the small freezer box from inside the unit, it's pretty well ready to go. I installed a couple oak racks, cut a couple of intake and exhaust holes and installed a digital temperature controller:
http://www.ebay.com/itm/310362192797?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649 with a thermocouple. I probably spent about $50 all told.
At first I purchased a cheap hotplate type burner from Amazon but found it was throwing out too much heat. I couldn't get it to give any smudge at lower temperatures, the fridge was just too well insulated. I then got a used George Foreman from the Salvation Army, salvaged one of the electric heat surfaces and wired it into my controller. It works just great, I can smudge while maintaining 120 to 130 degrees as well as take the smoker up to 170 if called for. I have even installed it into the corner of my basement and plumbed the exhaust and intakes thru some dryer ducts to the outside of my house, it seals pretty well, but the door seal is rather hard so I have to force the door tighter than the locking door handle will allow. I am planning on replacing the door gasket with a newer one before I give it another run.