Somehow, I don't think any dog would survive in such a box...
I believe there are lots of people that love dogs but can't have one full time (travel a lot etc); or who would happily take in another dog for a few days to keep their dog company. I imagine the price will rapidly approach zero therefore.
It's a great idea, but it'll be a very interesting marketplace to watch!
If you're serious, you can find my contact info in my profile.
I never would have thought it a problem because in my circle of friends there are multiple dog owners, and when one wants to go out of town the other just takes in their dog for the time.