the website is www.adrenalinr.com and if you try and purchase any muffler and change the quantity to 2 (as far as paypal ) this doubles the price.
For an example of an increase in price for an option go here productdetail.php?productID=518 and select the 101mm inlet size.
I've also attached my ecart1_php.php to see if that will offer some clues.
Thanks Jason