Get a set of two from Amazon for $5.99 (available in two colors).
Promising review: "I LOVE, LOVE, LOVE, these brushes! I usually used toothbrushes to help me get a good clean in small areas, but I found myself really having to scrub with them which did damage to the brushes. And when that happened, the brushes were then no good to me. I was moving out of my old house and had to get it cleaned to Military Specs as it was base housing, and I needed something to really help me get it cleaned. I found these brushes and thought, those might help me with the grouted areas, so for $6 I thought it couldn't hurt. As soon as I started using them, I just couldn't stop! I used them for grout, corners, cabinets, hard to reach places around my kitchen/bathroom faucets, around the base of my toilets, the inside of my windows, you name it and I cleaned it with them! After I finished my old house, I some how misplaced them and I was DEVASTATED! Needless to say, I ordered another set and began cleaning my new house with them. I have already recommended them to everyone I know and will continue to do so. These are one of my new favorite cleaning tools. I LOVE them, and could not praise them enough!!" —Katelynn C.