The New Zealand Herald: Discounter suspends fee to lure more on-line buyers: "Internet shopping club Go-Shopping has dropped its $14.95 a month membership fee for the next six months. [...] When it launched in November the membership fee was $24.95. In March that was reduced to $14.95 - ostensibly to build a buying group of 30,000 users which Mr Gordon said would provide enough buying clout to get even better bargains for its members. Now membership is free."

Maybe you have to go to the other side of the planet (I'm posting from France) to find a site that switches from fee to free. There again, it's a matter of critical mass before you can realistically charge your visitors.