I need a Dynamic Order Form?

Hi,
Does anyone have any idea how to do a dynamic order form? Let me explain.

Someone goes to my website and wants me to create a website for them. I have always had trouble charging them the right amount so i wish there was a way the customer could find out how much it will cost for them without having to contact us for a quote first. Therefore i thought some kind of form might be a good idea.

They select what they want. For example, they tick boxes saying:

Website Design - £75
News Page - £25
CMS Integration - £50
1 Page - £25
2 Pages - £50
3 Pages - £75
6 Pages - £150

Etc.

Then on each thing they select the form (or something) adds it up, and at the end, brings them with a total price of what it would cost.

Anyone know how to do this?

Thanks.

 

How's this?

<form action="#" onsubmit="return false;">

<p>
   <label><input type="checkbox" name="item" onclick="update(this.form)" value="75.2" /> Website Design - &pound;75</label><br />
   <label><input type="checkbox" name="item" onclick="update(this.form)" value="25.69" /> News Page - &pound;25</label><br />
   <label><input type="checkbox" name="item" onclick="update(this.form)" value="50" /> CMS Integration - &pound;50</label><br />
   <label><input type="checkbox" name="item" onclick="update(this.form)" value="25" /> 1 Page - &pound;25</label><br />
   <label><input type="checkbox" name="item" onclick="update(this.form)" value="50" /> 2 Pages - &pound;50</label><br />
   <label><input type="checkbox" name="item" onclick="update(this.form)" value="75" /> 3 Pages - &pound;75</label><br />
   <label><input type="checkbox" name="item" onclick="update(this.form)" value="150" /> 6 Pages - &pound;150</label><br />
</p>

<p>
   Your Total: &pound; <input type="text" name="total" id="total" size="10" value="0.00">
</p>
</form>

<script type="text/javascript">
<!--

function update(formObj) {
   var total = 0;

   for (var i=0; i<formObj.item.length; i++) {
      var myItem = formObj.item[i];
      if (myItem.checked) {
         total += parseFloat(myItem.value);
      }
   }

   var cents = Math.round((total*100) % 100);
   var dollars = Math.floor(total);

   var moneyValue = dollars + "." + cents;
   if (cents == 0) { moneyValue += "0"; }

   formObj.total.value = moneyValue;
}

// -->
</script>

Code (markup):