However, if you'd like to use oils, there is a very comprehensive guide to distilling them in the articles and forums. That way you can make your own at a much cheaper price and much more powerful because you have imbued your energy unto them for a long period of time. I suggest you review the data herein; you'll be surprised at what you'll find.
I, too, am poor but that should not let you stop from practicing the Craft. Everything you need is at hand--all you have to do is the research and to look around you. There are variations on spells and therefore differ, so if one spell calls for one element, another may call for a different one but for the same purpose. For example, in a repelling spell rosemary may be substituted for rue.
And it goes without saying, the most important thing to possess is a strong and clear intent!