How much is it to neuter a guinea pig?

DO NOT, I repeat DO NOT nuder a Guniea pig, This causes them to get WAY over Obese, even when on Guinea pig DIET for the rest of their life. I Know, because at around the age of six my first Guinea pig, we got him castrated. He lived for a few more years, but ultimately died for obesity, even though he was rationed, and on Diet the whole entire time. We were constantly taking hims to the vet, but it never helped.