A little off topic, but if you buy one of these, you'll be very glad you did:
I favor a high quality brush. They make life easier and produce better results. That's not to say I won't use a fifty cent brush for small oil jobs when warranted, but anyway...
I tend to stick to Purdy, Wooster Alpha, some Coronas, and so on.
A paint guy recommended one of these a month or so ago:
Picasso brushes. As far as cutting an edge - like nothing I've ever used. Incredible brush. I free hand edged a pantry's trim with 3 doors and a built cabinet. It almost looks like a laser guided paint brush did the cutting, and I am not a pro by any means. My local True Value sells them.
A 2.5 inch sash brush cost me around $10. Can't remember the exact price.