You've possibly passed these up hundreds of times in thrift stores, and they're hidden gold.
There are many, many thousands of people who roast their own coffee. While many have commercially made home-use coffee roasters, many also use hot air popcorn poppers to roast coffee with very good results.
Two models of air poppers are highly favored by coffee roasters. They're both made by Westbend and both carry the Poppery model name.
By far the most popular is the original Westbend Poppery. I've picked these up at thrift stores for as little as five dollars and sold them on eBay for close to $40. I also use one to roast coffee. Here's what it looks like so you can identify it:
The Poppery II doesn't sell for as much, but they're much easier to find. I generally pay between two and four dollars for them and if they're in very good condition get around twelve to fifteen dollars for them. Here's the Poppery II:
When you list these, be sure to title your listing as follows:
The Poppery air popper and coffee roaster
Poppery II air popper and coffee roaster
This is important because the search term for them is usually 'coffee roaster'.
These sell easily and they're so easy to find in thrift shops that it's worth the time to check around and see if any are on the shelves. If a plug is available, plug it in and make sure it heats up. You'll make coffee roasters who might not have access to thrift stores in their communities very happy, and make a little cash on the side.