Personally, Adam, I think it would be nicer to offer it via random selection from all those sharing photos, rather than having the photos judged. There's a wide range of skill levels in these forums, and more will be encouraged to enter if they know they're not being judged on ability. The K-70 is an attractive camera not just for already-capable enthusiasts, but for those just taking their first steps into serious photography too...
You could possibly stipulate that the photo must be taken
during the contest, and / or suggest a quite specific but easy-to-achieve subject matter (perhaps with a seasonal theme). That would be good encourgagement to get folks to pick up their cameras (whatever they may be - any make and model) and shoot, and would make for fun viewing
Whatever you decide, Adam, that's yet another very generous prize. What a lucky community we truly are...