Some of these clinics do rats and guinea pigs - ASK THEM
Some provide services FREE based upon your income or if you are caring for feral cats or they have grant money. JUST ASK.
Most of these clinics offer other low cost services at the time of the spay/neuter such as: deworming, microchipping, heartworm testing, nail trimming, flea prevention, etc. Check out their websites for more info and prices.
do NOT contact me with unsolicited services or offers