I have an allergy to soy, but I bet soy milk and yogurt would work just as well as coconut milk. Coconut milk can be found by soy milk and coconut yogurt can be found by regular yogurt in the dairy aisle in some supermarkets.
I don't like to buy expensive gluten-free flour; you can go to a store with a good bulk section and mix your own. I find rice flour mixed with oat flour is a good substitute for all-purpose flour in most recipes. You can prepare a regular graham cracker crust if gluten isn't an issue, and use butter instead of margarine.