There's an assortment of quality bags at a good price over at LA Police Gear. I bought the deluxe range bag for a diaper bag. My wife filled it up with enough for a two day trip and then didn't like how much it weighed, so now I have another range bag. I love it. The deluxe version has the removable ammo/gear divider and two padded pistol cases. I have some small pistol cases that I also put in the side pouches. I usually carry 4 guns, ammo, mags, and range gear in it easily. It's as close to perfect for what I want that I've found.
http://www.lapolicegear.com/la-police-gear-tactical-gear.html