The cheap slices you can get in New York are tiny (like 14" pies cut into 8), and they're made with crap ingredients, then baked on screens in conveyor ovens by people who know nothing about pizza. Real NY slices (in Manhattan) cost $2.50 to $3.00 per cheese slice. Unfortunately a lot of the real NY slice joints have gone out of business. Like Ray's of Greenwich Village on 6th Avenue & 11th Street and Ray's Pizzaria on Prince Street.
The state of pizza in Manhattan is not pretty. I spent a week there last fall, eating exclusively pizza from slice joints (as well as a couple slices of cheesecake). There are only two slice joints that I thought were any good: Bleecker Street Pizza and RayBari. I heard good things about Sal & Carmines (I think that's what it's called, at Broadway & 108th, maybe), but their pizza tasted like salt. I bought one cheap slice from a joint near Times Square, and I'll never buy another one.
Cheap slices in New York are not NY slices, OK. It's not a price war, either. It's just crap pizza. New York is not the same pizza city as it was only a year and a half ago, and it probably never will be again.