In my opinion, there are no truly good, cheap brushes. Every cheap brush I had, I threw out because it ended up being no good. Sonia Kashuk included. I had a couple of her brushes, and they both fell apart within a month of me buying them.
I'd say just buy one good brush at a time, slowly build up a collection. That's what I did. The only cheap brush I use now is a concealer brush from Everyday Minerals, and even that's getting thrown out as soon as I can get my hands on a Wonder Brush from UD.
I like ELF's smudger eye sponges (think that's what they're called), because it's just like a smudger on the end of some eyeliners, but by itself. I don't really consider those brushes, though. Kinda hard to screw up a rubber smudger!
Anyway, I'VE had bad experiences when buying cheap brushes. I would just say buy one good quality brush at a time, when you can, and eventually you'll have a nice collection.