It all depends on the building and inventory in that building. Co-op prices can vary considerably from building to building, block to block. Pre-war/Postwar, etc. If you can be more specific on block/area, I can give you updates of recent sales. email me at: http://www.elliman.com

Carnegie Hill is one of Manhattan's most prestigeous neighborhoods. It is primarily made up of pre-war coops, townhouses and mansions. The coops between Park and 5th Avenue in the 80's have some of the toughest boards in the city. It is difficult to get an average price per square foot in coops because the square footage is not always accurately reported in coops. Per room might be a better barometer of a fair price. The median price per room in the 3-Q of 2007 between Fifth Avenue and Lexington Avenue from East 80th- East 96th street was $250,000 per room.
However, being near Central Park and having a view of Central Park are completely different. A view of Central Park can cost 50% more than the exact same apartment in the same building facing the back.

I generally don't work up there but it looks easy to spend $1,800 per square foot in the Lucida, the new green condo going up on 85th Street.

Co-ops will be cheaper (buyers generally prefer not having to go through a co-op board) and it looks like some contracts are going through at $1,400 a square foot, while it looks like some things are going begging at $1,100 per.

So it depends on what your definition of a "nice" apartment is. Other things being equal, you will pay more for a family-sized apartment (one with at least three bedrooms, or at least that potential), a killer kitchen, renovations that are already done, a more prestigious building, the blocks just off the park, and a condominium rather than a co-operative organization.

Hope that gives you some guidance -- and if you're going through an apartment hunt in New York, you might enjoy my book.

Alison Rogers
author, "Diary of a Real Estate Rookie"
Insider Real Estate Tips with a Twist of Humor: http://tinyurl.com/2ag28z