Sum totals from multi-select dropdown columns

I have two columns with multi-select dropdowns. I would like to add a column that will sum the totals based on what is selected in the two dropdowns. Here is what I am trying to accomplish:

Cost List column: sandwich - $5.00; drink - $1.50

Optional Cost List column: icecream - $1.50; chips - $2.00

Total Cost to be charged: $10.00

What formula should I use to set this up to automate?