The price is set by the advertisers, not Commission Junction
CJ is just a marketplace that gathers together the publishers and pay per action advertisers. Instead of companies creating and running their own affiliate programs, they instead use CJ to do all the aspects of running an affiliate program — attracting publishers, setting up tracking codes, filtering abuse, paying the publishers, etc
Microsoft Live for example used to offer $5 per lead, but changed it to $1 per lead
GotoMeeting has a different price if the lead gives a credit card or not
The commissions are determined by the advertisers, and CJ does not dictate how much they should pay the publishers