Amazon.com has Tide Washing Machine Cleaner for $13.36+ FREE shipping with Subscribe & Save.
Be sure to use the $0.50 off clickable coupon below the item summary.
You can also use the $2 0ff coupon on the high Efficiency brand and pay about $8 each.
There are also several other Tide varieties on sale. Just scroll down to the suggested items on the Tide page to check them out.
Check out the previous Amazon deals.