It's a bit outside of GTA, but Yorkwood Veterinary Clinic in Keswick does inexpensive neuters - $78 including tax, but not including pain meds to take home, nor antibiotics, so that is a bit more.
The vet that has been doing neuters for me since last summer is Dr. Abdelmalek, but he is not experienced with treating rats for anything else. Dr. Manley was on maternity leave and she is back this Thursday and she has a bit more experience with rats (as well as neuter surgeries). The clinic staff are very friendly.
Also if you ask for pain meds to take home (metacam) I think their prescribed doses are way too low, and the Baytril was in a weird concentration - 10 mg/ml so I had to specifically request that they adjust upwards (this was Dr. Abdemalek) but I didn't have this experience when I brought a rat to Dr. Manley for antibiotics for a URI.