I always bought as much as I could stuff my freezer with when I had only two small baby corn snakes and my boa. Okay, maybe that is a bit of an exaggeration. Not really a large collection then but the closest place for me to get "good" "cheaper" feeders is two hours away. I usually bought enough to hold the snakes for two and half months. Snakes grow quickly and having left over stock was something I wanted to avoid so it wasn't like I bought enough for the year.
I am not really sure where you are located but I by mine from Canadian Mouse Man who is from Medicine Hat AB.