Like in any market, the prices are determined by what buyers are willing to pay for a property. This is dependent on the comparable prices with other properties that have sold in the building, and then checking to compare with how much money apartments have sold similar buildings in the area. This is exactly the type of information a Licensed NY State Real Estate Broker would do research about, in order to help their clients.
I wish I could say that Real Estate Brokers had a significant influence over prices, but in reality, the market determines the prices. That being said, I strongly believe that prices have been lowering in units that were for the most part, overpriced. However the question you are asking is really much more complicated than you may have originally believed. This is because even though there might be an average price per square foot that prices have fallen, to get the answer that applies to the type of property you are interested in getting information about, you would really need to be able to identify which buildings are similar in the neighborhood as far as time when it was constructed, building amenities, location to public transportation, etc., etc. Again, a Licensed Real Estate Agent will be able to help you figure all this out.
My best recommendation is whatever you decide to do, you should know that if you plan on looking on your own, when you answer ads for apartments for sale, you are responding to ads that are placed by the Seller's Brokers'. These people are hired by the sellers to get the highest price possible for the apartments they represent. Since a commission is going to be paid by the seller anyway, and it costs you absolutely nothing, you should have your own representation, in the form of a Buyer's Agent.
Senior Real Estate Sale Associate