If you want to calculate a more precise total amount for the resource in question, you can use the Resource Detail pane.
Before you can select items from your budget, you (naturally) have to establish your project's budget first.
In the logframe, click on the resource in question. In the Resource Detail pane, you will get the following table:
Select as many budget items as you want. The total amount will be shown in the Budget column of the logframe. If you've entered an indicative figure there, it will be replaced by the calculated total of the budget items that you selected.
This way you can establish a clear link between your activities, objectives and budget. This will allow you to show for each output how much money you intend to spend. You can do this by printing the Resources table.