OP: You should post an address for donation. Either to offset your cost, increase the reward to the 13 winners, or to increase the number of prizes available. You pick, but I think you'll see a lot of us support this effort.
I will do that after I pay the rewards at the end of this competition. I do not want anyone to think that I will take the donations and run without paying. If anyone decides to donate at that time, I would use those proceeds for another bitcoin promotional effort.