I would say 3-600 is typical. Most of the cost involves critical care monitoring, (BP, EKG, Pulse ox, apnea alert, CO2 level) anesthesia, IV catheter/IV fluid administration, a designated technician/nurse monitoring vital signs, hospitalization, preanesthetic blood testing, and a designated nurse monitoring recovery. $85 dollars wouldn’t even cover the COST of the medications needed (including inhalant gas through an endotracheal tube). There are additional fees for extractions based on how much time they take, if a gum surgery is needed to remove them etc. Then there are post op medications , typically antibiotics and antiinflammatories if extractions were needed. Intraoral radiographs are essential for diagnosing dental problems. If your veterinarian doesn’t have them, find someone who does.
This is truly a case of ‘you get what you pay for’. I have heard of people doing dental cleanings with injectable only anesthesia (no endotracheal tube). You should ask if your vet does this (especially the ones charging $85) because it puts your pets life at risk. I have heard of people not using IV catheters - which would jeopardize the pets life as well, should anything happen during the procedure that required emergency medications or fluids.
Ask a LOT of questions, and satisfy yourself with the answers before having your pet treated. If your vet doesn’t use one of the procedures above, ask why. I would be very wary of anyplace that was charging less than $300, and I wouldn’t have my pet treated there. There are veterinary dental specialists - maybe you could talk to one in your area, and ask what general practitioner they would recommend for routing cleanings. (or ask what the specialist charges for the same)
Then do whatever you can with homecare to try to prevent the need for frequent cleanings. “Healthy Mouth” water additive has the veterinary dental seal of approval, meaning tests were done that showed benefit. Brushing is great, if you can do it. Bones are ok, but some dogs do break their teeth on them. Genetics play a huge role too, so some of it really is out of your hands.
Good luck!