Amazon [amazon.com] has 44-Count Efferdent Dental Appliance Cleaning Tablets for Retainers and Dentures (Minty Fresh & Clean) for $2.02 - 30% off when you 'clip' the coupon on the product page - 5% when you check out via Subscribe & Save = $1.31. Shipping is free w/ Prime or on $35+.

Note: Coupons are normally one use per account, possibly targeted, and YMMV.