With orders of $25 or more, Amazon offers the Mr. Clean Magic Eraser Cleaning Pads 8-Pack for $6.28. Clip the $1 off coupon on the product page to cut it to $5.28. Plus, Prime members receive free shipping. (Non-members can spend $35 or more to qualify for free shipping; otherwise, it starts around $5.) That's the lowest total price we could find for this quantity by $7. They purport to work with water alone and can be used to clean appliances, walls, floors, and other surfaces.

Note that this item is part of Amazon's "Add-on program" and can only be purchased with an order of $25 or more.