I am trying to create column that will return the total cost of item selected in a multi item drop down list. The price of the items are on another Smartsheet. I want the other sheet to stay separate so that it will be easy to change the cost later down the road without having to restructure the formula.

Basically I have a form for an equipment order where the user can select multiple items needed, I want a cost column to return the sum of all items selected in the equipment column so we can email this to the requestor.