I think prices should be mentioned at some point before a surfer hits the credit card form, such as on the final tour / "join" page. I've always imagined that if you send them directly from "JOIN!" links on your tour to a page like this
http://www.furrygirl.com/ccbill/index.htm surfers would be wary to click those links. Not everyone understands how internet billing works, so they might assume that clicking "Instant Credit Card Access" would "bill their account" or something, without having a chance to see the price. I see that so often, though.
(I realize this only applies to paysite owners, but I still thought I would share.)