I'm not too sure about in NY, but here I just get them from the pharmacy and they are cheap. Buying them in a low carb section would definitely result in a higher price...
Because I'm diabetic and have a 'prescription' for them, I actually get an official prescription receipt and can claim it on my insurance. If your dr is supportive and willing to write you a scrip for them, you might be able to too, depending on your drug plan, of course.
I also buy the Diastix... you can test your drink in a restaurant to make sure it's really diet. You'd be amazed how often it's not, and there are times I'm not paying enough attention to the taste, by the time my stomach tells me, it's too late...