That rule of thumb of 35% off the retail price may work for a normal retail shop situation, but it may not be right for a handcrafted product not sold in a brick and mortar store.
The advice I have been given and what has worked well for my small custom/retail/wholesale manufacturing business (not soap, by the way) is pretty much what Eshell wrote:
Cost X 2 = Wholesale
and
Wholesale X 2 = Retail
If I choose to reduce my wholesale or retail markup for a particular situation, I can choose to do so, but these rules of thumb work pretty well most of the time. We've been in business for 12 years now, so I'd say something is working right.
I want to add that the "Cost" is not just my out-of-pocket material costs -- it also includes labor at a fair wage and including US social security and medicare costs and overhead such as taxes, insurance, utilities, etc.
If you don't want to include those fees, that's your choice, but keep in mind if you go wholesale, you need to be asking a truly fair price for your product, because it's not just a hobby business anymore. I can tell you it gets old dealing with all the headaches and working long hours if all you're getting back out of the deal is minimum wage and just breaking even on your other expenses.
--DeeAnna