Amazon offers the Fresh Guard Dental Device Cleansing Soak 24-Count for $3.29 with free shipping. That's about $2 under what you'd pay at a local store. They're designed for retainers, mouthguards, and removable braces. To get this price:

1. View the Fresh Guard Dental Device Cleansing Soak 24-Count for $5.48
2. clip the 35% off coupon on the item page
3. checkout via Subscribe & Save for a final price of $3.29

Be sure to cancel Subscribe & Save once your order ships in order to avoid being billed for subsequent shipments.