Manufactures don't like it when I call their tools cheap, but there's good cheap and bad cheap. Bad cheap is when a tool isn't worth what you paid for it, even if it only cost $1.29. Good cheap is when a tool costs very little but does exactly what it's supposed to do, which would be an excellent description of Rockler's Silicone Glue Brush.
The tool consists of a plastic handle with a flat spatula-like spreader on one end and silicone bristles on the other. The bristles are about 1/16" in diameter and very rubbery. Glue doesn't stick very well to silicone, so if it dries on the bristles, it's supposed to be easy to peel it off.
I've had one of these brushes since last summer and have been using it to spread yellow glue, polyurethane, and epoxy. It's convenient to have a glue brush that can be reused and does not have to be cleaned after each use.
The silicone bristles hold a reasonable amount of glue and are stiff enough to spread it as thick or thin as necessary. If the glue is particularly viscous or needs be spread where the bristle end won't fit (it's about 3/4" thick), you can spread it with the flat end of the tool.
Carpenter's wood glue can be removed from the bristles by soaking them in water or peeling the glue off after it dries. Dried glue comes off easily — usually in a single piece. Unless you're willing to use some gnarly solvents, it's best to wait for epoxy and polyurethane to cure and then peel them off later. These glues have more grab than yellow glue, but if you pull hard enough they will come off the bristles.
As an experiment, I allowed Gorilla Glue (a brand of polyurethane) to cure into a large blob around the bristles. I had to pull so hard to get them out I was sure some of them would break. None did, but they left their impression in the glue.
The Rockler Silicone Glue Brush sells for $4.99 and is worth every penny — which makes it the good kind of cheap. The brush is also available in a kit that includes a flexible silicon glue tray and notched spreader. I haven't tried it yet, but if the kit is anything like the brush then it's definitely worth a look.