i looking for something that pay for example 50$ per action... (eg trial sign ups) is that possible ?
very possible, many including hosting cpa's pay more than that. Usually though with that higher ref earning means that your customer needs to put up decent cash for it to happen.
To get that much, you are going to have to refer people that pay. It's easier to just promote offers that will get you $1-$2 and in bulk. Think about it. You can refer 1 person in a day and get $50, yes, but it's harder to get them to take the action. Or you can refer 50-100 people in a day and get $2 (total 100-200 dollars) for them filling out a form that requires them to not pay a dime. Take the friction away, don't make em pay. That's the way I do it. Just run multiple campaigns at once and you'll see the payoff.
have you tried e-mail submit offers, they pay abt $1, you can get them from most CPA networks, I've had good success with them from 365adsolutions.