I picked up a black Adidas bag from Dick's Sporting Goods. It holds my size 10 shoes perfectly (and has a vent on the side for the... scent), my indicators, hat, sunglasses, brushes, soccer-style shin guards, jacket, keys, cell phone, etc. It's got good height, which makes up for the fact that it's a 23" bag.
For a fast-pitch or modified-pitch umpire with larger leg guards and chest protector, it might work. Depends on how long those leg guards are.
The one I bought is
here. For $30, it's not a bad deal.