A best bet is the Vitacost 15-35 Probiotic 240-Count Jar (pictured) for $49.99. (Choose this option from the dropdown list.) Add it to your cart via Set & Save and activate the above coupon code to drop it to $38.24 and bag free shipping. That's $12 off and the lowest total price we could find for this supplement. It contains both pro- and pre-biotics and aims to promote digestion and a strong immune system.
Be sure to cancel Set & Save once your order ships to avoid being billed for subsequent shipments.