Here's some ideas
I found that Wal-Mart has the cheapest price in coconut oil. It's in the baking aisle with the other cooking oils. If I remember, it's in a 32 oz. can for right around $5.
Castor Oil can be found in specialty stores or may be at a farmers market. A lot of times, they'll have hard to find oils that you may not find at the local grocery store.
As for olive oil, there's a place in Phoenix, AZ where I live that's called Smart & Final. It's a smaller version of a food wherehouse (like Costco) where some restauranters (and the general pulic as well) can go to get their food and cleaning products. I bought a gallon of extra virgin olive oil for under $10. So I don't know if there's one where you're at (or anything comparable).
Hope this helps.