I don't buy cheap ones. Shedding is a nuisance and the quality of the bristle influences the quality of the brushstroke.
Turpentine is extremely destructive. Cleaning brushes destroys them, they wear out more from cleaning than from painting. So I don't clean my big brushes. I keep them in a bucket full of vegetable oil. I only wipe them off, squeezing out most of the paint, avoiding turpentine as much as I can...
