title: Pass a form field to a URL
body: <p>I am not a developer but have been asked to integrate Paymate 'pay now' buttons <a href="http://www.whitewreath.com/donate--shop" rel="nofollow">into a website</a>.</p>
  
  <p><a href="http://www2.paymate.com/pm/default.asp?title=Website-and-Cart-Integration&amp;contentID=68" rel="nofollow">Paymate has an ajax form to generate the code</a> which is in the form:</p>
  
  <pre><code>&lt;a onclick="self.name = 'parent';" target="_blank"
      href="https://www.paymate.com/PayMate/ExpressPayment?mid=&lt;username&gt;&amp;amt=&lt;amount&gt;&amp;ref=&lt;reference&gt;"&gt;
  
      &lt;img src="https://www.paymate.com/images/ebay/paymate_accepted_logo_88x31.gif"
          border="0" alt="Pay with Paymate Express"&gt;
  &lt;/a&gt;
  </code></pre>
  
  <p><code>username</code>, <code>amount</code> &amp; <code>reference</code> are all variables input into Paymate's link generating form to generate a live link to paste into the source code.</p>
  
  <p>My problem is that there are two items to be sold that come in variable multiple quantities.</p>
  
  <p>I need to produce a form field which accepts a number, and on entering this number, the URL of the Paymate button needs to be altered dynamically, so that amt is the correct figure.  e.g. 25 items @ 3.50 each.</p>
  
  <p>I don't know how to go about this.</p>