It varies dramatically. For example, With Lucky Nugget, I had 203 clicks this month and 62 depositing players. While with Grand Prive, I had 142 clicks and 11 depositing players. Most of my casinos fall somewhere in between. However, I find that my click to deposit ratio is often far below normal with 3rd party groups. For example with Trade Doubler, I had 149 clicks this month and only 3 depositing players. Pearl Gaming has been a notable exception to this 3rd party generalization. I have had a better than average click to deposit ratio with PG.
Of course the ratio also depends on your site. If you have a review giving detailed information about the casino, the click/deposit ratio should be lower than with a banner and little information