I bought one of these for about $30 on Amazon. One small benefit is that the shape doesn't scream GUN.
UTG Covert Homeland Security 34-Inch Gun Case
I'll second this case. I have the 32" version and it's just long enough to fit the 15-22 with the stock fully collapsed. In hindsight I would have gone with the 34" version -- other than that I've been quite happy with it. FYI - plenty of room for a mounted scope and it has internal straps to keep the weapon from shifting around during transport.