I work in right here in the Garden City area. Assessed value often doesn't have much to do with the actual value of the house. In fact, prices are on the rise here in Garden City.
There are a few different things you could do, and I'd like to talk to you more about them.
Please email me at JeffGushman@gmail.com. Let me know the address of your house, bedrooms, basement/etc, and how much you owe, and I will see what houses are going for in that part of town.
Look forward to talking to you!
Century 21 Castelli