Thanks for considering options. The value should be dependant on quality, technique and detail of the artwork. What some project owners have done is stay with the guaranteed fee and increased it for the winner on completion. I'll submit a sample in a day or so. Thanks

The winning designer will only see about $80 out of the prize money. That's barely 6 dollars per illustration, where a single illustration of quality could take an artist anywhere from 6 - 10 hours. That's barely a dollar an hour for all 12 illustrations. I would encourage you to award the winning designer based on one sample and then work out a fair fee for the remaining illustrations afterwards.

Best of luck with your contest!