I'm going to NYC soon and i wanted to taste "real jewish food" when i go there. can anyone tell me about a good place that's not too expensive and that offers jewish food but not mediterranean but more like russian or polish?

Unfortunately, all kosher restaurants in the city will cost you a pretty penny, you may find a few gems though, check out this page;
http://www.citidex.com/6461.htm

Katz's Deli, 2nd Ave. Deli (it's on 33rd st. now)

Sammy's Roumanian Steakhouse, kinda expensive, though.

http://nymag.com/listings/restaurant/sammys-roumanian-steak-house/

Caroline's on First Ave. in the East Village is Polish but not Jewish. Veselka Ukrainian restaurant in the East Village.

http://newyork.citysearch.com/profile/7087313/new_york_ny/veselka.html

There are a few Glatt Kosher Restaurants in the Garment District.

Sammy's Romanian is a good choice but expensive.

You may want to venture to Brooklyn for some good spots

Mill Basin Kosher Deli
Adelman's Deli