I was there a couple months ago and all you had to do for the 99 cent Margs was go to the small back bar near the sports book and purchase them there, no coupy required.
The last time we were there - in December - the front bar also had the margaritas- they are the best!!!!!! along with Big Elvis!!!!! The bartenders are great there!
I love bill's. I know it may not have the best Craps there (hopefully they do still have live craps as I read somewhere they are doing it on a machine now) but playing craps and listening to fat elvis is a blast!