Seconds ago i checked 7search bids for "online casinos" for you and the top 6 listings are all bid at over $4.00 and some months it's over $5.00 . Plenty of their related keywords are bid at $2 or less.
I don't have gambling sites but i make it my business to know who's advertising what.
If you know how you are going to generate revenue and have an idea of how many visits it should take to see your most wanted response then you should be well on your way.
I'll sticky mail a few possible solutions but the key will be to start small and test test test.