There's a new restaurant that I believe is the cheapest in Chinatown. It's the Central Buffet @ 195 Centre St. But it's not tourist fare. They claim to have 100 different dishes (seemed more like 50), but it's a fairly exotic selection. It's a great way to try new dishes. The quality is good and the food fresh. You get 4 dishes and soup for $4.00 but after 6pm it's an incredible $3.00. The customers are 99% Chinese. I think they close by 9pm.
Check it out and use all the money you save to go on a ChowMarket shopping spree.