since you already have about 20 pages of plans to display, just make a function that would pass the filename of the plan you want to load into the iframe...
if your iframe code has an id of plan:
<iframe id="plans" src="about:blank" width="400" height="400" frameborder="0" scrolling="no"></iframe>
document.getElementByID('plans').src = 'http://potternet.duoservers.com/plans/' + plan_id + '.html';
then you'd just supply the file name without the htm/html/php extension right in the link like this:
then you'd just need to make sure that you have files named 36906.html and 36901.html
you can also use jquery's load function to load the contents of pages into the current page into a div for example, but not with an iframe.
so you see, too many ways to skin this cat