I am such a little hypocrite. I suggest that people buy nice makeup brushes because I like nice makeup brushes, and I think that they make a serious difference in application. And then when it comes down to having to spend on nice makeup brushes myself, I am so good at talking myself out of it.
To be fair, I think that nice brushes are essential for certain things and less essential for other things. For instance, foundation needs a good brush, as does applying/blending shadow in the crease, and contouring cheeks. But I think for things like blush and applying shadow in a wash across the lid, you can get away with cheaper brushes.
This Sonia Kashuk brush I picked up today in Target was either $4.99 or $5.99, and it's not on the website. Here's something sorta similar. It has a white handle, and it's about 5 inches long, which is a nice, usable length. I'm 99% sure the hairs are synthetic, but I mean for $5 I can't complain, and they're a decent sort of synthetic. As y'all can see, the brush is a stubby little thing with a rounded head, and pretty darn narrow.
As for how it works, I'd say it's pretty decent. It works better with some shadows than others--it failed with my MAC Lusters, but did pretty well with my more pigmented, less shimmery shadows. What I really wanted this for was to help apply my MAC Pigments, and it's just perfect for that. The application can be a little blotchy unless you're careful, but it's pretty easy to get an even wash of shadow across the lid.
Conclusion: For $5, this brush is a good deal. Is it as good as a MAC 239? No. But it's $20 cheaper. If you want something a little nicer, I'd recommend the Sonia Kashuk brushes with the black handles and real hair, which run about $13.