Javascript Math

So I want to add a little dynamic touch to my order form. First of all, I don't program in javascript, but I can take a script and modify it to my needs. The form I have basically has all numeric values used for calculation a grand total price.

Here is an example: http://www.xibitony.net/order.php

Play around with it, but what I basically want to do is eliminate the "Calculate Cost" button. Could someone write up a quick little example as to how to accomplish this? Thanks!

You have to provide more details like how the calculation is done and other important information needed in order to come up with the cost.