Did you know that your average EBR will fit into a 3/4 sized electric guitar gig bag with room to spare? The gig bag comes with backpack straps for hands-free carrying, and the accessories pouch will hold enough ammo to deal with the zombie apocalypse. Typical price is $14-$25.
One caution, the tactical accessories on your EBR should be limited to a small to medium sized scope and maybe a flashlight, although the flashlight can also live in the pouch. If your rifle is fitted with headlights, tail lights, turn signals, and a winged lady hood ornament, all bets are off.
Update: Starting the new year off with an Uncalanche! Thanks Unk, and it can only get better from here on out.