Total Cost Based on Date of Task Being Finished

I am working on charting out dev tasks and need to display what our expected total monthly cost would be based on the tasks finished each month. I am struggling to find out a good way to have this either permanently displayed or easily accessible. I have tried reports but that only displays all of the costs and does not total them. If I create a filter the same thing happens. I want our exec team to be able to look at the project and see how much our cost would be each month without having to click around and do a bunch of math. Is this possible?

PS: If there is a way to have the total costs of tasks finished appear in gantt view it would be ideal.