It doesn't matter what you've spent if the rodents have spoiled and your snakes end up sick or die.
On the positive side, I purchase my rodents from the same company--excellent product. So long as the mice arrived frozen (with dry ice in the box), then the company is not at fault. If they thawed after they arrived, due to a power outtage, or accidentally being left on the counter, then you may have a problem. As meat thaws, bacteria sets in quickly.
Assuming that they are not spoiled, I think I know the smell you are talking about. Adult frozen dead rodents have an odor that is different from pink/fuzzy frozen dead rodents. And if you thaw meals for 20 snakes in a big pot of water like I do, that odor is quite the norm. It is also the odor that perks up everyone in the herp room.
Do you know anyone else who keeps snakes? Sharing box space with someone else will cut your costs. Also, if there is a herp society in your area, get involved. You may meet folks who can ease the financial aspects of snake keeping. Best of luck!
althea