You can find information about spay and neuter vouchers from animal protection organizations such as SpayUSA and Be The Solution. Individual city or county animal control services may also provide spay and neuter vouchers for citizens of that area.
Spay and neuter vouchers are certificates sold by counties, cities and organizations that pet owners can buy to cover all or part of the cost of a spay or neuter procedure for their pets at participating veterinarians. These tend to range in price from $5 to $50. Nationwide organizations can provide lists of spay/neuter voucher programs and veterinarians that accept the vouchers.