Unless you are selling knives every day, skip the electronic machine. I have a non-cancellable lease, to the tune of about $30/month on mine, and I have never used it.

The best deal I got (finally, after having been burned a couple of times) was by joining the local retailers association ($70/year). The handle all my credit card transactions, the details of which are the same as Jonathan's.

Worth doing if you are serious about selling your work.