I think using any product that helps eyelashes grow can help your brows grow as well. For a cheap option, I've heard of some people having success with castor oil. Ardell's lash serum is also well liked.
Not sure if lash products i.e. RapidLash would work. If you're looking for a great brow pencil, Shu Uemura has a lovely one that has great staying power.