In the Southwest, I can get a 1/2 gallon of Coconut Milk http://www.purelydecadent.com/products/coconut_milk_beverage.html at the Sprouts Market. http://sprouts.com/home.php $4.59/ half gallon.
And here is a blog for making your own coconut milk. http://nutrition-and-physical-regeneration.com/blog/533/how-to/how-to-make-coconut-milk/