>Is this truly the going rate for the area? Has something substantial changed in veterinary medicine in the last decade that explains the cost?

There's a few things happening here:

1. High cost of doing business in the Boston area (as others have pointed out, the price drops off once you get outside of 495)
2. There's a nationwide shortage of veterinary workers which has also driven up costs

Your best bet is to search outside the city as others have suggested. Animal Rescue League and the MSPCA do offer subsidized spay and neuter services but both have months long waiting lists and limit their services by income, breed (e.g pit mixes), and/or zip code of residence.