Restricting Estimates

Restricting Estimates

I am looking for a way to enable specified user roles to:
  • Have the ability to create estimates
  • But not have the ability to change pricing (or better yet, have a defined range of allowed change) 
  • Not be able to create new items
When i have tried to change the permissions, it does not work right for me. The role still ends up being able to override the price with any value...