The Tanner home is depicted as one of the Painted Ladies on Steiner Street facing Alamo Square (Google Maps).
Zillow lists them at between $1.15 million and $1.82 million. Exactly which one the Tanner bunch lived in was not said (I don’t think), but a likely 4-bedroom candidate is at $1.55 million.
Fraiser was a psychiatrist that means he was an MD (or DO) and a specialist at that. That is a very well paid field. On the sitcom Cheers he appeared to have not only a private practice, but was on staff at a research university and various clincs.
At least on Cheers he would’ve been well paid. His clients were probably Boston’s Back Bay elite.
Now I don’t know on his own program if he still had a private practice or not.
Frasier’s apartment still pared in comparison to the diggs that Niles had. He lived in a GOTHIC MANSION with Maris, and then got a pretty insane apartment after he got divorced (which had stairs, a library, and a room just for his parrot). To his credit, there was an episode where Niles had to take a closer look at his budget, and temporarily moved into a shitty apartment with a bed that folds into the wall.
The Malcolm in the Middle family lived in a very modest ranch house (where was never said, but they didn’t make much effort not to make it look like California). If not for the inflated nature of California real estate, it’d be a realistic house for a family of their means (basically one income, spread between four, then five kids). However, I think they showed a flashback that had them buying the house in the 80s when low to middle middle-class people could actually afford real estate there so maybe we can consider it a rare realistic house.
Maris’s family was definitely rich. I remember the family business was something of an embarrassment to Maris, though I can’ remember what that business was.
IIRC, at the divorce settlement, it was revealed her family made the little deodorant tablets that go in urinals.
Wikipedia says the Maris family fortune came the urinal cake business. That must have been revealed after I lost interest in the show because I have no memory of that…
Coke to BiblioCat 
But the Huxtables are doctors and lawyers, not waitresses.
The Eppes home on NUMB3RS has been featured in many publications; it’s a 100-year-old Craftsmandesigned by the Heinemann brothers. I can only imagine the value to be in the $3M range.
The OP asked what was the most valuable sitcom property - not which property was most disproportionate to income.
The King of Queens house really bothers me for some reason - it just seems too nice for a couple of their means. Anyone know what standalone, two-story houses go for in Rego Park, Queens?
I guess Magnum, P.I. doesn’t count as a sitcom? Because that is one hell of an expensive property.
Yes, but no one pretends that Thomas Magnum could afford that place. It’s understood that he lives in the guest house of an estate owned by a mysterious millionaire, in exchange for providing security.
Given that, I nominate Boris’s house from Royal Pains. It’s not a sitcom, true, but the house itself costs more than every single other nomination in this thread combined. Heck, the GUEST house probably comes in second…
That mansion The Beverly Hillbillies lived in was probably affordable on their means, but still had to be expensive even in the late 60s…
How about the Banks’ mansion on The Fresh Prince of Bel-Air?
The Adams Family Estate had to be several million…
For example, $439,000.
If they did buy in 1989, it was during a downturn in the market
I would guess they paid $250,000 in 1989, less if it was in “fixer-upper” condition and they did the work themselves. I believe the mortgage payment on that (6.5% 30 year fixed rate, 10% down) is about ~$1450. It would be tight at first but doable on two ~$35,000 salaries. The Wife, working in a white shoe law firm environment, probably made more than that but I’m being conservative.
Well if we really stretch the definations of “property” and “sitcom” then the Jupiter II of Lost in Space is surely a contender. An interstellar spacecraft that’s the product of a coalition of industrialized nations. It must have cost a fortune.
And sexual favors. Mmmm hmmm.