In addition to the Double Four recommended above, if you don't mind used, you should be able to pick up a nice used Phil Jones Flightcase and definitely a Bass Cub within your budget. If you must have new, the Double Four would be a good choice. I picked up a mint used Flightcase for £350 a couple of years ago and it was excellent. I only sold it because I later bought several small PJB cabs, any one which, with a small class D head, makes a fine home/practice rig, so the Flightcase was surplus to requirements.