1. A computer-implemented method, comprising: detecting a link selection event in which a user selects a link on a web page of an originator web site of an originator entity to access a target web site of a target entity; in response to the link selection event, programmatically causing the user to be charged a first fee and the target entity to be charged a second fee, said first and second fees being based on a linking campaign of said target entity; calculating a monetary amount to be paid to the originator entity in connection with the link selection event in accordance with said linking campaign, said monetary amount being greater than the first fee and greater than the second fee; and programmatically causing said monetary amount to be paid to the originator entity in connection with the link selection event, whereby the user and target entity each contribute to a payment made to the originator entity in accordance with said linking campaign; the method being performed by a service provider computer system that is separate from the originator web site and the target web site, said service provider computer system operated by a service provider entity that is different from the originator entity and the target entity; wherein the monetary amount is calculated by the service provider computer system by summing the first and second fees to generate a total contribution amount, and by deducting from said total contribution amount a transaction fee charged by the service provider.