I'd say a $15 silver-tip is probably not going to be a quality brush. Most any badger brush that looks like it's packed tightly is going to serve you well as a first brush, but for a real quality silver-tip, you're going to pay more for it than that. Keep in mind that even the reputable brands all use different terms for their different qualities of hair as there's no standardized rating system.
I wouldn't go boar or synthetic.