Some places do offer low-cost spays/neuters so I wouldn’t be terribly worried. Have you asked them how many they do a month/week (depending on how big they are)? Their success rate (>99% is ideal)? Those are important questions to ask.
Nothing needs to happen prior to the procedure really. Just remember that rabbits are not fastest before surgery, so don’t take away her food. You can bring some food for her along to the vet so they can offer her some afterward. Most bunnies are pretty out of it when you first bring them home. Many vets will give a long-lasting pain injection, which is sometimes sufficient for boys. For girls, it’s always a good idea to ask for additional pain meds for when the injection wears off. Obviously, a spay is more invasive and they will need more time to recover. Keep your bunny comfortable and let them rest for a few days. Remove anything that might entice them to jump. If it happens to be a 2nd level in a cage, then find a way to block it off. Hopefully that helps some.