Hi Vegas_Player
One should realize that values listed in price guides or books are estimations published by the various authors based hopefully on sound research and time consuming record keeping. These prices do not represent absolute values and are definitely not up to the minute due to the time difference between gathering of data, authorship, publishing, acquiring of the published information, and the discovery of the particular strike that one is interested in buying. Therefore, one should view these estimations with a grain of salt and they should be used only as a starting point as to what one is willing to pay for the strike.
The primary determining factors affecting the values of strikes are RARITY, AVAILABILITY, and DEMAND. DEMAND is inversely proportional to RARITY and therefore nothing else needs to be said. AVAILABILITY is a horse of a different color. The higher end strikes are primarily a sellers market due to RARITY and if one is to acquire these strikes, deep pockets will be needed or maybe one can just hope to just get lucky and find one at your local flea market.
For your information, the New York, New York $10 (Key to the City) G mm, has sold on E-Bay, which represents the closest current values for strikes, in the past six months for: $252.49, 203.38, 200.00, 191.38, 212.00, 174.50, 197.50, 180.27, and 162.50. The average of these numbers, for the mathematically disadvantaged is $197.11.