Pearl Paint, on Canal Street and Broadway. I went there all the time in highschool. Take the NQRW or 456 or JMZ (or 1, A, C, or E, but it’s a short walk) to Canal Street. It’s like art mecca. The prices can’t be beat and they give students 10% off. (I also have a tax free card there, but shhhh)
Blick Art Materials
Located at 1–5 Bond Street. That’s 1 block north of Bleecker, between Broadway & Lafayette St. (you can take the #6 subway to Bleecker and then walk). Make sure to sign up for their free members’ card so you get a discount on every purchase + mail discount coupons. I just received one for 40% off a single item, good from 8/22— to 9/7. It’s yours if you want it (consider it a Welcome-to-NYC-gift LoL)
I don’t know where you can find cheap art supplies, but there’s nothing on earth like your first few months of living in New York! Live it up! Enjoy the City!