Actually, shipping lenses back and forth isn't that big of a deal--just get the borrower to pay shipping and insurance back and forth and have an agreed upon borrowing period. Back in the spring, I borrowed another forum member's Sigma 10-20 with a similar-type of arrangement and it worked out just fine on both ends.
BTW, I checked with CameraLensRentals.com and they are planning on ordering a Bigma next time they go lens shopping. I'm going to Tennessee to my parents' in December and Dad and I may go out on a birding shoot, so a Bigma would be nice to have for that trip.
Heather