I've got an Ortlieb Velocity, and I love it:

http://www.ortlieb.de/_prod.php?lang...odukt=velocity

comfortable padded straps, totally waterproof, plenty of room inside. Also 100 percent pick-pocket proof if you ride the subway or bus sometimes. My only complaint is that there's no place to clip a blinking taillight on it.

Not sure what "reasonable price" is for you, but it costs around 100 bucks.