I've been using a Stir Crazy / Turbo Oven (SC/TO) style unit for several years now. I only do 1# batches in it and usually roast 2 batches every two weeks.
For those not familiar with this style - the popcorn popper bottom provides the stirring mechanism while the turbo oven top provides the heat. A springform pan ring provides the spacer between the two. I've built a few of these for others and I usually average about $75 total in cost for them.