This is way too vague a question. Do you want windows included? SmoothDaddyFig's old b13 SE-R was down to about 1800-1900 lbs, which is the lightest I can remember.
the stock weight of the B13 SE-R is around 2460 and the NX with t-tops is 2580. With what you mentioned you would be 500-600 lbs lighter. Maybe a bit more with no windows.