Covering hosting costs is a good idea. But really paying for hosting wouldnt put affiliates off it is getting the site quickly available to the players which would be most beneficial. Advice on which content areas to target plus putting the content together in regards to the game your affiliate programs supports would help.
Covering hosting costs would be a good incentice but could prove difficult to actually implement. Other incentives you could offer are prizes for affiliates suh as holidays, free laptops etc for affiliates bringing in losts of layers. Money is obviously great but prizes really help to!