I recently just broke down and purchased a chest freezer and started to buy Frozen Thawed rodents in bulk online. I have plenty of room for the freezer in my basement, but it sounds like you're lacking in indoor space for a freezer.
The freezer I purchased claims to only increase electricity bills by $26 a year. I'm sure it would cost a bit more to keep the freezer in a garage, but I bet you'd still save money in the end by buying 6 months of rodents in bulk online (must buy in bulk to make the shipping costs worth it.) And... Can you really put a price on the peace of mind your hubby will have knowing your rodents are far far away from his Lean Cuisines in the family freezer!
You could also purchase a lot of live rodents locally and gas (see the DIY forum) and freeze them yourself to possibly save even more with a freezer.