Actually, I have a random idea.
1. Get some cheesecloth (or something similar that is just as soft), and place it in the bottom of the tub.
2. Fill tub with water and big-ass fish
3. Take tub home, place next to your tank.
4. Pull up cheesecloth by corners, trapping fish. Water will remain in tub, fish will not.
5. Put cloth/fish in tank, let go of the corners, remove cheesecloth, the fish remains.
That's what I would do, given my rationale and budget.
EDIT: In the scenario in my head, this would include removing water from the tub once you got home, and replacing it with your tank water and acclimating the fish, of course. You'd just have to do this in the tub rather than in your own tank. Water out, water in, no biggie.