A spay/neuter surgery is not too terribly expensive and well worth it. Thank you for caring enough to do this for your girl! Without knowing where you are located, I can't say for sure, but here in the Northeast it is about $125 for the surgery, and $60 for preliminary blood tests to be sure she/he can have anesthesia. I would say it probably does not vary all that much across the country unless you are in a remote area You can check with your local rescue organization or even Petco, they can help you obtain lower cost spayings as well.
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