Once upon a time, I had a coupon for a free children's bath product. I have no idea where I got it from, but I used it on one of those foam pump soaps for kids with tear-free body wash inside. The soap is long gone, but I kept the pump. Pampered Chef also sells a version too, but it's cheaper if you buy the version in the kids' bath aisle (I found mine in the baby aisle). If you're worried about wear/tear, I can tell you ours has survived for several years and still works well.
You can often find $1 off 1 coupons for Johnson's Baby shampoo. Frequently, there are no exclusions on size. Many stores sell the travel sizes for 97 cents -$1.07. So, very often, my kids get free soap. One travel-size shampoo mixed with water will fill the entire pump. So, anywhere from free to 7 cents, I get an entire supply of tear-free soap for the kids.
For more great ideas, check out Works For Me Wednesday at We Are THAT Family!