I've been roasting for quite a few years now. Here's my first roaster. It's a modified Mr Poppery (original version). These particular air popcorn poppers have a 1500W element which is more than adequate for roasting coffee and are very well built. The modification consists of removing the thermostat and wiring the blower onto a separate plug. One can then control the heating element with a variac. With some experimentation, you can get very good roasts out of this thing. I've found that peaberry beans roast very well in it. The can is from a large can of chicken broth. The chaffe is blown out during the roasting process so there's little fire danger at all from darker roasts.
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The Mr Poppery is a very inexpensive way to get started. My second roaster was a Behmor 1600, my third a Hot Top.