WARNING! THIS IS NOT ACCEPTABLE BEHAVIOR. YOU MAY GET BANNED FOR DOING THIS! It is still a "solution" though.
Since KoA is such big paying mission that everyone does, I figured, let's stop players from doing that all the time. How? Simple. Start a party for KoA, then after everyone has gone down to the first area, kick everyone from your party. They ALL go solo. Repeat as often you can.
There is a problem though, players who actually need to complete this mission, are unable to. Sorry, but fixing the economy seems to be priority #1 around here.
WARNING! THIS IS NOT ACCEPTABLE BEHAVIOR. YOU MAY GET BANNED FOR DOING THIS!
Better idea: Remove Mission GUI