Virgil's, which is delicious but pricey and packs a big caloric punch. I've blogged about Flavrz before (favorably) so I was delighted to find their organic root beer syrup in my local grocery store. Just add seltzer. And it's only 35 calories per 8-ounce serving.
I had to try it. My husband also happens to prefer root beer but has been sticking to flavored seltzer as he's on a health kick. I had a feeling he, too, would appreciate a more natural, lower calorie option. It's sweetened with agave nectar, which I happen to love in beverages, as well as a little stevia.
So, we both tried it and agree that it's an inexpensive, delicious treat. I think it was about $6.50 for the bottle and you get 21 servings per bottle at the suggested dilution. Add five 1-liter bottles of seltzer at $.60 each and you're looking at $.45 per 8-ounce serving.
They also make cola and ginger ale syrups. If anyone tries them, let me know what you think. Cheers!