Make fields clickable to sum up data

I have an excel sheet that is used for pricing out new inventory. I want to be able to make all the fields clickable so that our sales guys can click on the options they want and have it sum up the cost in a box.

I want the salesmen to be able to click "Coloumn A" or "Column I" and have it populate with a check mark. I then want the data that is in "Column G" and "Colum O" to be sum'd in a box at the bottom giving a total price.test.xls
Thanks
Matt

IS this even possible?

---------- Post added at 12:45 PM ---------- Previous post was at 12:35 PM ----------

I have been able to put a box in each field that when clicked on puts a check mark in it. Now i need it when the box is checked to grab the data from another cell and sum all boxes that are checked into a cell at the bottom of the page.