The unit next door also indicates $421 per month. There is a lower unit that is about $260 a month, but as indicated, that is a considerably smaller unit.
So yes, it appears the dues are $421 a month.
1. Some I've seen have had extensive grounds. Two in particular were somehow connected to a golf course area. In neither case did my client have enough interest in the property to investigate further (e.g. did golfing rights come with paying the dues).
2. In some instances an association will borrow rather than have a special assessment, and increase the dues for a period of time to cover the borrowing. In such cases it might be possible for the seller to pre-pay the increased amount at closing, but note that there is some risk there if other owners default.
3. Some older units cover heat and even hot water. I used to live in such a condo and I wouldn't be surprised if the dues are now over $260 for a one bedroom unit, and well over that for the largest units in the building.
4. Personnel. If there's a 24 hour doorman, someone has to pay for that, and it's the owners.