A circle always have accountabilities, which are defined in the super circle's governance.
These accountabilities would normally be distributed to roles within that circle so that the roles can execute them. Since a Circle is merely a grouping of roles, circles can't by itself execute anything. Anything that is to be executed has to be done by the role fillers of the roles in that circle.
Having said that, you can have roles work together to decide something, as long as it is clear what decision making method you are going to use. This is at least how we do it in our organization.
In your example, I would perhaps define a policy on the "All functions and activities within the circle" or one of the appropriate domains the circle has that says something like "Budget Decisions shall be made by the following roles by voting: role x, y, z"
The method used can be whatever is more appropriate. As Dennis indicated above, one option is to use IDM, in which all objections are integrated, instead of voting, just like in governance. With IDM, all concerns or objections are processed and good enough solutions searched for together. With voting, the concerns or the choice of the minority group does not get processed, and a "third" alternative is not searched for.