I just signed up today (free) and have sent an application to one of the companies who want you to place their ad's on your site.
Just apply. Been with them for over a year. I would not join an affiliate company that charges a fee.
Hi, You apply under "publisher" if you want to become an affiliate and sell for others. Most of the advertisers will not accept your application to be an affiliate for them if you run an incentivized site or a website with some incentives that attract them to sign up, so make sure you fulfil the conditions when you apply.