There are at least 2 to 4 salons per block from W. 135 St to Dyckman St.
You will not have any difficulties locating a salon.
If you are looking for cheap, there is one spot I often visit on/around E. 115 St between 1st and 2nd Ave. It's called Magic Touch. It's a little ghetto but they do okay work. They charge a flat rate of $10 for a wash and set, no matter what kind of hair or how long.