Certainly call the Humane Society nearest you, and ask if they know of low-cost spay/neuter programs. It will be healthier for Hallie in the long run to be spayed as soon as possible, and you are a good person to be concerned about this.

In fact, do you have a regular vet? Maybe you could volunteer there, or at the humane society, in exchange for a lower-cost spay for the dogs? It's worth a shot. The Humane Society folks would rather help you, I bet, than risk more puppies being born into an over-crowded world.