SPCA, APS, humane society, SNAP, cheaper vet clinic, to start. Just make sure whomever you choose doesn't skimp on pain meds. If you're going to bother putting them under general anesthesia for surgery, it doesn't make sense not to control post-op pain.

If it is still before their first heat cycle, doing it now saves you a 100x rise in possibility of breast cancer later in life.

In the Los Angeles area you can get discount vouchers for spay and neuter of rescued animals ($30 off each for up to three cats), and even more off if you qualify as low-income. Certain vets accept the vouchers, not all. In our area several good vets known to me will give the discount.

Where do you live?

Do you have friends who are low income?- why not just give them the puppies have them take them in to get fixed calming its there pets, you give them the money YOU pocess and thats that- drop off that vet- when he asks about puppy shots- I'm sue vets by now are used to the i got a dog lets re home it gig. You save money animals get fixed thats better then honesty in this case IMO.