http://www.vitacost.com
has great prices on many probiotics (and other stuff too!). One way to test your probiotic for "activity" is to open a capsule & pour the powder in a cup or so of milk (I think whole milk is best)....let it stand at room temp overnight...if it is like yogurt by 12 - 24 hours, you've got active bacteria! I do this from time to time to QC whatever brand I happen to be using at the time. I also make my own water kefir which I KNOW is active! :-)