Thanks to Sarah for this Frugal Baby Tip!
I recommend this to all my patients with severe diaper rashes. It is sold under that brand name and if the store doesn't stock it you can have them order it.
You can also make basically your own version. Don't necessarily know which is cheaper, but if you can't find the original this will work just as well.
1 tube zinc oxide or Desitin
1 tube Aquaphor (sold under that brand name)
1-2 tablespoons of Burrows Solution (this is the magic ingredient in my opinion)
Burrows Solution is sold under the brand names of Domeboro or Pedi-boro. It comes as a powder that you mix with water. The extra solution is excellent for soaking a raw bottom. For little ones you can just put them in a baby bath with the solution, for older kids you can soak a washcloth and have them hold it on the rash as a soak. It's great.
Mix those three ingredients together and voila. Some people don't like zinc oxide to get on their dipes, so if you are worried about that, you could use a fleece liner or something. Hope that helps.