You need to find out what exactly that $750 entails and what is included - everyone thinks, "Oh, it's just pulling 2 teeth!" but depending on the age and the health of the cat, there is preanesthetic bloodwork that should be done, anesthesia, IV catheter with fluids, pain medications, antibiotics, dental radiographs (x-rays), extraction of whatever teeth need to be extracted (which usually involves having to use a high-speed drill to make it easier and making sure all the roots come out, so it's not just "yanking them out"), cleaning/polishing the remaining teeth, etc. When my husband had to get a root canal done, we did not have dental insurance at the time and we were quoted between $500 to $800 - when people have medical insurance, they typically are not aware of what things actually cost, it just gets billed to the insurance company. But then when people have to pay for the equivalent for a pet without insurance, it seems like a lot.
It also depends on your area where you live and how progressive of a vet practice it is. Some vets are not totally on the up-and-up when it comes to the latest recommendations for pet care, including taking dental disease and pain management more seriously. You can try getting some other opinions, but keep in mind that probably at each different practice, they are doing to probably charge an exam fee to see your cat, come up with a treatment plan and a cost estimate. And like I said, not everyone is doing the same level of work. I admit, it always irks me when people think because Vet A only charged XXX to do a dental cleaning or spay a dog, that Vet B is ripping people off by charging people more. But maybe Vet B is being more proactive when it comes to anesthesia safety and pain control. Or especially with dentals, some pets have minimal issues and it's just a straight-forward cleaning, whereas others have significant problems and the work is a lot more involved. What you were quoted does seem high to me, but I don't have enough information to totally make a judgement call.
I would try to clarify what exactly your cat's care will include and entail, and then see also if they are able to give a low-end and a high-end for an estimate. But can I tell you if it should be done? Probably it should, because no animal should have to live with chronic pain, but also I am not there to look at your cat, and without an exam and dental x-rays, I can't say for sure.