It sounds like you're pretty ok to get it in Summer and store it. A big tight stack will stay fresh in the middle even as the outside picks up some moisture -- dry hay will probably act as a dessicant for you!
If you're looking for organic and cheap, I recommend buying some out of the field after baling - you can get a good loock at it, only take the bales you want, and know exactly the kind of farm it came from. If I
sell hay out of the field, it's just $100/ton instead of $160/ton out of the barn...
You might also look into a trailer of alfalfa being delivered..