More than likely they are going to want to do pre-op blood work, and then the spay and you'll want the pain meds, because face it, if you're getting cut open, wouldn't you want to have the pain meds. Animals feel the pain, so they do deserve the extra couple bucks (or a movie ticket) that the meds require.

The vaccinations, except bordetella, should be mandatory. Rabies especially.

I'm still floored that there isn't any shelter organization that offers low fee stuff.