like Hamuko said, there are domains like .party, etc that are cheap. However, some sites won't take them. My main junk account is a wildcard .party domain. It'll work with mosts sites, but the odd one won't take them. I ended up registering a .com that goes to the same inbox to get around these.
Sort by cheapest renewal.
For example, you can register and renew a .feedback domain for $1.49 a year.