Might want to start looking under the fenders and near the spare tire. Perhaps the previous owner left a hide a key somewhere on the vehicle. I keep on inside my frame on my truck for instances just like this.
Also, if you have AAA, or a friend that has it, they'll come pop it open for free. If you aren't the one with AAA, just get the friend to come over, and say y'all took the truck and he's riding with you.