right/left click on cell, do some math, show result in pop-up

I'm wondering if this can be done; I have a pricing spreadsheet that contains a very long list of prices on products that ppl buy and/or cell simultaneously. I currently have a scrap cell where I add or subtract the prices to see how much the prices net out to. For example a client might want to buy two widgets for $1.00 each and sell one $0.50, this nets out to $1.50 the client has to pay.

I'm looking for a way to make this more efficient and have the results displayed in a pop-up box or form. Also, I'd like to have the left click represent addition (+) while the right-click represents subtraction (-).

so in the example above, I would left-click twice on the $1.00 price, right-click once on the $.50 price, then press Ctrl-P (or whatever) and a pop-up/form would spring up with the resulting price, $1.50.

Srry for the long winded post. any help would be much appreciated

x-posted: http://www.mrexcel.com/forum/showthr...57#post2472157