Need new tires and want to get a bit more clearance (taller tires): questions

Hi. It's soon time to replace my 95 Astro tires. Presently I have the standard issue/recommended tire size of 215 /75 R15 on them. However, I've been desiring a bit more clearance on the van and've heard that taller tires is one way to accomplish this. Even an inch higher would be an appreciated improvement. But I'm wondering if any taller tires will lower the mpg (very important to me), or mess up the odometer accuracy (important too, tho' a bit less so). I also want to get tires that are decent and durable on the many rocky roads on which I take my camper-van to boondock...so, like, maybe something in the better traction/high performance spectrum? I don't encounter much snow or rain in the landscapes I roam, but yeah, it's often in/out on dirt roads where many rocks abound. Oh, and also, I don't wanna spend a lot of money - my budget is around $100 a tire. Any tips and/or recommendations of size or brand are welcome. Thank you.