Some SEO contests are quite cool Imo.. There was one last year with the theme “global warming awareness”, which can’t be bad (and which made it easier for participants to get links due to the “good cause”).
Interestingly you can expect to make A LOT more cash that 1st prize pays if you do this for one of your own projects rather than for a subdomain which will end up making your “enemies”/competitors richer in the long run.