you need some sort of place to hold the beneficial bacteria that will sustain the livestock you will be keeping in this tank. this is the function of live rock. live rock, generally porous, holds bacteria on it's surface, and in the pores, which help to process the nutrients you and your fish will be adding to the tank.
you might try checking the local craigslist and other local bulletin boards for people breaking down their tanks(there are always a few), and buy some rock from them. generally, they sell it at a decent discount.
i have heard that in NY, lr
is pricey..but only an hour and a half away or so from you there is a large reef store that sells live rock for 2.79 a pound(uncured).
it's a decent drive, but i think it's worth the trip to check out the store.
pm me if you need the address.