Get ye to a gun-shop and figure out what feels the best. Don't assume two guns of the same manufacture or even of the same model will be exactly alike. There is a world of difference between my 590 and a Maverick 88 and there is a world of difference between an 870 Express and a Marine Magnum. The cost, while not immaterial, should not be the deciding factor of a gun you will choose for protection. Unfortunately, you will not be able to determine if the gun is completely reliable until you have had the opportunity to use it, but once yours the gun must be proven reliable. If there are any hiccups in loading, feeding, ejecting, or firing; those must be ironed out prior to going afield.
Do not disregard a semi auto out of hand. The semi auto will not short stroke thus leaving you unarmed. The semi auto's solid forend provides a stable sighting platform unlike the pump. The new inertia operated autos appear to function reliably with ammunition with a broad range of power levels. Of course the price of these is about 4X outside of your budgeted price, but they are worthy of consideration if you can afford them.
My choice of protection gun was a Mossy 590. You can take it from me, the need for big magazine capacity is over stated in a gun you intend to carry around for protection. A 9 or 10 shot magazine makes the gun too heavy, too bulky, too long and too slow to get into action. My 590 is nearly perfect other than the unnecessarily long magazine and barrel. If I had it to do again I would choose a gun with an 18" barrel, conventional stock, 5 shot magazine, sling and swivels, and a ghost ring and post sights. Imagine any defensive shooting scenario you care to. If you have not solved the problem within 3 rounds, you probably will be unable to, and you will not solve it unless you can get the gun into action.
