Every realtor is going to tell you that there is no way to determine that since it all depends on how accuratley the condo was priced in the first place.
A quick way to do it would be to calculate the price per square foot that you paid and then look at the avg. price per sq ft. in that zip code. ( now depending on where you bought that could be a wide area) JC varies a lot block by block so its tough to get an accurate reading. Furthermore, the condition of the condo you purcheased( amenities, upgrades, even the floor it is on all play a part in determinig the market rate).
Since you are buying in this market you are investing for a while( holding your property for 5 years or more). After 5-10 years its really not going to matter if you overpaid slightly for your property. Don't stress out, owning a home is a good thing. I'm looking myself. It's possible that over the next year you are going to see prices come down even further( but we are only talking a few percentage points. )
As long as you are happy with the place and will enjoy living there you shoud be cool. The tax benefits alone make it worth it to own versus rent in the JC/Hoboken/NYC marketplace. Plus if the sht ever hits the fan and you can't pay your mortgage you can always rent out the property rather than foreclose. (The rental market is and will continue to be strong in this area) .