500,000 thousand diamonds - holy mackerel Batman - that's a lot of Ice
I doubt anyone with any level of common sense would ever go that bonkers, but hey, maybe someone is crazy enough to bite on that kind of an instant military boost?!
...iirc, by completing the entire quest line + daily log-ins + collecting all incidents, it's suggested you'll enough up with around 190-200+ total ingredients, which provided you're careful in your baking, should be enough to gain 4 selection kits via the grand prizes.
Add 2 kits from the quest line milestones + 1-2 more depending on league finish, and for 0 dias, a player should be able to acquire 7-8 selection kits for building their choice of fields.
That's still enough for say, 1x bench + 2x ochre + 3-4 wheat fields for a solid attacking army boost.