I love making home-made soap out of fat and lye. It's not actually a very good money saver, as soap is very cheap to buy but soap-making ingredients can get pricey. They don't have to be pricey, but when you get really tempted by the nicest-sounding essential oils and speciality fats and waxes like me it's hard to hold back.
Still, I find it endlessly satisfying to make things myself. Just knowing how to make things, rather than depending on buying everything at the shops, is pleasing. Maybe I'm weird but I just don't find instant gratification all that gratifying.
So I make my own soap in batches and use it or give it away or barter it. At the moment we're using an unscented hemp-oil soap, and a few weeks ago I swapped a bar for lots of packets of veg seeds.
I wrote an article about soap-making, and the nice people at selfsufficientish.com published it here. It's got a recipe, detailed instructions, and several very fetching photos of me.