Simple Calculations

Are these possible with webforms, or can they be made possible? I checked out E-Commerce and its way overkill for what I need. I have a user who takes orders on friday for lunch from a local sandwich shop (Very important stuff you know :). Currently he tallies everything in a spreadsheet. I created him a webform so people can order online. The form contains the all the things they can order, and any special requests. I would like to be able to have the cost of the items automatically calculate out w/tax & delivery (we have a standard formula for that built in the spreadsheet).

Is there any way to have a numerical field (in my case called item cost), and then a "calculated" field which figures out the cost for each submission?

Obviously E-commerce is great for a large "product" type environment, but it just seems way too much for a simple task such as this. I imagine people could greatly benefit from having such a feature.

Thanks!