Lol get the 0.5 oz - I promise it will last a month or more. I think the super large ones are for ppl who do businesses of making soaps or perfumes or etc.
Most of the 0.5 oz is only a few dollars too unless you get an extremely rare one (like 100% rose oil).

I can relate to the money issue though. Are there any programs you can get on there that can help you with any of your financial needs?