I have worked as a vet assistant for 5 1/2 years and am getting my vet tech degree now.
It depends on if the hernia can be reduced or not. If there is just fat in the hernia it is no problem. If there are abdominal contents in the hernia it will have to be repaired. If it is a female it is usually done at the same time as the spay and not that much additional cost since you have already paid for the anesthesia, hospitalization and pain meds. If it is a male basically the same thing but there will have to be 2 incisions and usually with the female they can do the spay and hernia repair with one incision.