It varies from one season to the next and one week to the next. Really hard to say on average. Last year I was part of Netflix and BBC documentaries and went all out. I put 30,000 miles on my car in 6 weeks.
I just bought a Rav4 hyrbid and it should effectively double my MPG but I really needed something bigger for my equipment so now I'm dumping about $15k into it the mod work and outfitting in order to maximize MPG and cargo space. That's about $7k more than normal. My fuel gets paid for but I want to make sure it stays that way so it's why I'm making the change.