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You don't need a whole lot of flour to get a sourdough starter going. And all you need is flour and water. Or, for the price of return postage and an envelope, you can get some dried starter. Google Oregon Trail Sourdough and you'll get to Carl's website. When you get the starter, there are 2 sets of instructions. The one with potato water is for historical purposes. Use the other one.

@downhill, there are recipes that have you starting with a lot and doubling it and throwing away a lot, but you don't need to do that. If you don't want to use the not-quite ready mixture in a dough, you can start with two tablespoons of flour and two tablespoon of water, and before you refresh it, you take out half. Then add back a each of tablespoon of flour and water. At the most, you're tossing a tablespoon of flour, and it doesn't take more than a few refreshes before you have something lively enough to use. That's when you start doubling, so you have enough to make however much bread you're going to make. Of course, it gets better as time goes on, but you can still use it that young. When your container is threatening to overflow, you take out most of it, leave a tiny bit to continue the culture, feed that, and put it away. I have three different cultures living in my fridge now. With the stuff that you take out, you make bread. You still might need double it again if your original container is small, or it might be enough to get a loaf going.

I started my first wild culture in a pint mason jar and that's where it lives all the time, in the fridge, until I need it.