The 2 vets I worked for(2 different hospitals) both did a hernia repair no cost with a spay/neuter. I would say if you like the dog it is well worth it. You can also call the place you plan on taking her to and ask how much extra a hernia repair is. Usually they are pretty cheap because they are easy to fix.
Your best bet is just to call the vet and ask for an estimate, that way you have solid information to go with. Prices vary hugely- from an extra $20 to double the cost of the spay. Best to know for sure rather than guessing!
I would do it myself if I liked the dog since it's a one time thing, and nothing on the lifetime expense of any animal. Better to pay a little more up front to get the critter who is going to fit well in my life than cheap out on the start and wind up with an animal who will never be quite what I wanted/needed.
I think I'm going to get her depending on what I find out tomorrow. Exactly, and I've been looking for a while with no luck.