Specify setup price from direct shopping cart url

Hi Guys

I am setting up my website to allow the purchase of premium phone numbers which have a setup cost based on how good the number is. The site is Joomla but is highly integrated into whmcs. the website will show the available numbers and the price and then a customer will click buy next to one. There will be a large range of prices and I dont really want to have to create a product for each price. Is it possible to have a single product and specify the setup cost in the Direct Card URL?

If so could anyone give me a hing where to start?

Regards