Think about an upright freezer instead of a chest. They have the same foot print or smaller for an upright. With an upright you don't loose things. The bottom of a chest freezer can be scary. Also, don't buy a frost free model. It will cycle an thaw. So will the food in it. If you won't use it in five month get a vacuum sealer. That can make frozen food (rats) last years.
If your in the States others have already listed some suppliers that ship bulk. Get some friends together an split an order.
Now, one thing small hobby breeders forget. What happens to the rats if you go away for a week or two? If you don't have somebody to watch an check on them it's option two. Gas the colony an start over when you get back. Heck I know snake keepers that raise rats for six months. Gas them an restart after the summer. That fills their freezers.
Good luck!