I didn't think we'd paid as much as £21 at Sheffield, but I can't remember for certain.
Tatenhill is central, cheap, has a good cafe at weekends, and if I'm instructing, I can hopefully take a break and say hi. And if I'm not booked up in advance, you can have trial helicopter lessons if you like.
Derby is friendly, but has shortish, fairly challenging grass runways....not for all aircrafts or pilots.