Add Values In A Dynamic Table?

Basically the order form works this way (see attached image to clarify) - the user clicks on one table to select the price wanted of the product and this value appears in the second right hand table automatically.

So far, so good.

But I am trying to get a subtotal value that adds the cost of the products automatically too.

At the moment I am using this function to set the price in the second table:

function set_price(val, count)
{
var g = <?=count?>;
var eachValue = document.getElementById("price" + g);
eachValue.innerHTML = "£"+val;

[Code]....