It is really quite simple. Be like Nancy Reagan. Just say "NO!" It's not rude, it's reality. The gals know at most men are not happy to say no, so they play you like a sucker. But you need to embrace that "NO" word. Learn it. Live it. LOL!
Seriously, if it makes you feel better, use the phrase "not tonight" instead of "no." But use one of them liberally. You are the customer and it is up to you to decide for whom to buy drinks. They'll get the idea soon enough and the precedence will have been set.
Change bars (not bar areas if you don't want to), cuz it will be impossible to change modes in the current one now, and start over...