You can find stevia in health food stores, Trader Joes, some super markets, and on line. Some brands appear to cost less and even say things like 'all natural' but have some sort of filler.... I like 100% stevis as I think it lasts longer and is better.... so check the list of 'other ingridents' that is on the bottle.
You can find comparson ratios and charts for other sweetners and recipes on the internet.
If a person is diabetic it is far and above the best sweetener according to what I've read. It may even be healthy for them.