Multi-Select for a Transaction Form

Multi-Select for a Transaction Form

Form A
Product                     Price    
apples                       5.00
oranges                     6.00
bananas                     7.00
etc........
 
Form B is a  transaction with a multi-select (apples,oranges,bananas,etc.)
Deluge Script help 
If a customer were to buy more than one fruit, how could i get the total price of multiple fruit.
ex.  apples and oranges were purchased, the answer would be $11.00
 
Thanks for any help.