Sounds like you're going to get it fixed one way or the other. I can't really tell you which is the 'right' way for your dog, but definitely need to do something. A sore tooth/mouth is not a good thing for any one or any animal, especially a retriever. I imagine he'd retrieve just fine with 3 canine teeth instead of 4.
Extracting a canine tooth as a serious procedure. A healthy root on a canine is as long, or longer than the tooth. On the upper arcade you have to create a skin flap, grind away bone to expose the root, then extract the tooth and close the flap. Possible complications include an oronasal fistula (opening from the mouth into the sinuses). Lower canine extraction is similar with the risk being fracture of the mandible. I've done a few of both when I was in mixed practice and they generally required a fair amount of profanity before it was all said and done.
I've never seen a root canal/cap done. That's definitely a referral (specialty) procedure. It would definitely be what we call the 'ivory tower' fix.
I don't know what you were quoted for extraction, but I imagine it was also a significant amount, given the time and skill it takes to accomplish it properly.
As for vet costs in general, veterinarians as a whole aren't out to milk every penny from you. We are trained to offer the best care possible, sometimes that's not cost effective for a client, and that's ok. But imagine if you had the ability to pay for a $500 treatment that had excellent results but you were only offered a cheaper option with lesser results or you pet died. You'd probably be really pissed at the vet for not offering the better treatment am I wrong?
Yes, veterinary care costs more than it did 10 years ago, but so does everything else. Especially veterinary school. Students are routinely graduating with $150k plus in student debt. Tuition alone at TAMU vet school is about $25k a year for in state students. Higher tuition costs mean graduating vets have to make more after graduation to service this debt. This cost has to be passed along to clients.
In 1999, the average annual tuition at U.S. veterinary colleges was $10,668, compared with $28,504 in 2017, a 167 percent increase.
Additionally, clients, on average, demand a higher level of care than in the past. This often translates into purchase of specialty equipment. In the OP's example, 20 years ago the only option most likely be extraction. Root canals and caps were not very common place then.
Sorry for the off topic rant. OP, good luck with your pup. I'd offer to help but I don't even work on my own dogs anymore.