Vet recommended a full dental cleaning under anesthesia for my 4 year old beagle - is this normal at that age?

Took my beagle Hank in for his annual checkup and the vet said he has significant tartar buildup and is recommending a full dental cleaning. He's 4 years old and seems totally healthy otherwise, so I was kind of surprised. She's quoting around $800 for the procedure.

I've been brushing his teeth maybe 3-4 times a week which I thought was decent. The anesthesia part is what worries me the most - I've heard horror stories about dogs not waking up and I can't stop thinking about it. Is this something I actually need to do or is it a money grab? And is 4 years old young to need this?

Also asking because I saw some ads for anesthesia-free dental cleanings that are way cheaper. Are those legit or a bad idea?