I picked up a new unit on eBay a couple of years ago. There was a huge thread on KLOV about popcorn poppers so I followed the advise and got an 8oz kettle. Glad I did, it makes awesome popcorn.
The pre-packs make it so easy to do. Cut the oil side and squeeze it in. Pour in the kernels when it is hot and sit back and watch the magic.
A roll of paper towels sitting next to it helps make sure the grease doesn't get everywhere.
ken