It's tough to pay for an expedition. I learned that when I sold my jeep to fly to Arizona... and when I almost didn't get to the Gila Wilderness last year... and right now as I am attempting to get sponsorship for my current expedition (and you should probably follow me on facebook or twitter to keep up with the preparations!)
Luckily there are awesome adventurers like Al Humphreys to point us in the right direction! I was recently reading his blog when I found a post that he published recently. It contained many of the methods that I have used to save money for expeditions myself. Instead of repeating everything he said, I'll steer you over to his blog. There's really some great insight!