Puff is a little over three years old and I'm reading more and more about the health benefits of spaying, but I'm not sure if she is too old. She's very healthy with no history of illness. Also, what's the usual price range for bunny spaying??
She isn't too old, there really isn't an upper age limit as long as they are healthy. She should have an exam before surgery and even blood work done just to help rule out any issues.
3 is definitely not too old, but every rabbit should have a full physical exam before anesthesia and adding on bloodwork to check organ function is also beneficial. The cost of the procedure varies alot from location to location. One good way to find a low-cost option is by contacting local rabbit rescues and finding out what vet they use/recommend. Chances are they do a lot of rabbit spays and have a good price.
You shouldn't have any problems at that age, but you can always ask the doctor to do a blood panel and a full check up to determine is she is healthy enough to undergo the operation.