Since champions can't die; atleast not that i am aware of.  i think that they should have a maintenance cost that increases with their level.  however, this cost can be any number of things, not necessarily gold.  it could be that a particularly evil character could want population, or perhaps another wants food.

This could be offset with aligning your intentions with their motivations.  if you meet their motivations 100% then they are essentially free.  on the other side of the scale they could be very expensive to maintain.

if you can't pay their price they leave your service and wander about the land looking for someone that can pay their price.

this could help with some players ending up with a majority of the champions by a stroke of luck.  the main reason being that it would be really expensive to keep too many heroes due to conflicting motivations.

there could be many factors that could determine motivational personalities.  good, neutral, evil, warmongering, peaceloving, greedy, poor, highly magical, non-magical, and i am sure there are others.

thoughts?