This obviously depends on the quality of traffic, not the quantity.
A casino will make any type deal it knows it can make money on.
At this time I am only aware of the phoenician offering perclick routinely, and I am not sure what the per click rate is. I think cashforclicks still offers it too.
Personally, I prefer deposit based, or commission based, although I am not opposed to media buy models of any description. I do some fixed rate ads, but I do not do perclick or CPA deals.
I think the most money is to be made on a percentage deal, and fixed rate deals tend to make up for natural fluctuations.
But again, it depends on the quality of your traffic. Overture traffic was very high quality and hence they could charge that kind of money.
How many clicks would be needed on average to land a real player? That is the big question.