Hi Mary,
The price they're quoting seems really fair. If she's 13, and you're happy to, I'd ask for her to be put on I/V fluids. It helps the anaesthetic, help the kidneys etc, and makes for a faster recovery overall for the older cat. They will no doubt keep her on the fluids the remainder of the day so she'll get the full benefit. I know at my mid-priced practice they charge clients £50 for I/V fluids, so it should be cheaper where you're going, plus you'll get your discount. It's really nice of them to offer instalments... not many vets do!!
I am sure she'll be absolutely, 100% fine
I've nursed 20 year old cats, and they've been fine under anaesthetic! It's really good that she has no underlying health problems, too. You could also ask for a tin of AD wet food to bring her home with, if they have it. Hi calorie, great post-op food. Great for a recovering patient!
I know she'll be fine... and the lump'll be nothing to worry about, I'm sure. The op won't even take long... so her anaesthetic'll be quick.
Have a relaxing weekend with the lovely Bonnie...
Liz x