I've read through these posts and wondered if there was anything I could say that would contribute to the information already gathered. I'm not sure, but I'll try.
Right out of the gate I found the question a bit disturbing, because you say that you want a cheap gun for protection in the back country. Cheap is a subjective word, but to my mind it means junk. Junk tends to be unreliable, and perhaps even dangerous to use; so why would a man want to to waste his money on junk when for just a little bit more he could have a tool that would provide him with not only pride of ownership but also with durability, reliability and real security? Isn't this the gun that you intend to stake your life on? Perhaps the word you were looking for was value. Many of the posters must of read it that way in that their suggestions for the most part are not for cheap guns.
For several years I packed around a cut down 12 gauge single shot equipped with rifle sights. This was not for the consideration of cost, (which was surprisingly high by the time I got the little gun to where I wanted it) but it was light and handy to pack around in difficult country. It proved to be less than ideal when I actually found myself in a dangerous bear situation and grudgingly I got a pump to tide me over until I could get a suitable rifle. (I had lost all of my guns in a house fire) In the time that passed before my rifle was completed, I had carried the shotgun hundreds of miles on my back, and had 3 dangerous bear encounters that were resolved without blood. That gun is a real confidence booster. I find it is more useful close to town than is the rifle, and in one situation that occurred in pitch darkness I would not of traded it for the rifle.
The process leading up to my decision of which pump to choose was somewhat convoluted, but I began with the premise that I wanted an absolutely reliable, conventional butt stock, allowances for a sling, 18"-22" barrel, rifle sights, a tough finish, and a slick action. I had every intention of getting a Remington 870 Marine Magnum until I began to wonder if it was in fact the best choice.
Mossberg was in the midst of advertising their milspec 590 so I took a look at this to see why the military would prefer a Mossy to the snazzy Remington. What I found was the gun that met all of my requirements. It's parkerized finish was resilient to the elements, and would shrug off scratches. The winged ghost ring was the perfect rear sight, too bad they didn't wing the front sight as well, and I did end up bending my front sight. Most importantly, you can swap out any part without sending the gun to a gunsmith. Try to replace the ejector on an 870, that's right you can't without specialized tools, but on the 590 all you need is a screw driver to complete the task. The action after a short break in period is slick enough that when the gun is held muzzle up, unloaded and cocked, the slide drops back under it's own weight when the release is pressed.
The temptation is to take the opportunity to save a few dollars by getting the Maverick 88 instead of the 590 and those who are promoters of this idea point out that after all, it is the same action . A fellow I work with came to this conclusion, but when you put the two guns together, the differences are astonishing. A big consideration is that the Maverick has a seald magazine like the Mossy 500's. I've never been a fan of that arrangement as there seems to be no suitable way to clean the inside of the magazine tube. Where my 590 is slick, the Maverick is rough and requires a great deal more effort to work the action. I want to say that the Maverick has a single action bar, but I don't remember if this is in fact the case. I just know that operating the gun was much more difficult that was my 590. The Maverick has a cross bolt safety rather than a tang safety, but this is of little importance beyond personal preference. The barrel of the Maverick is blued, and blueing is less resilient than parkerizing, nickel, or stainless.
Another fellow at work bought the Marine Coat 500 with both the pistol grip and the conventional butt stock and the short barrel with a bead. His action was also much better than the Maverick's, but again the 500 has a sealed magazine. His first problem was that fired shells failed to eject, and the gun had to be sent out for warranty. Upon return he had no further issues with reliability. He tried to shoot slugs with the pistol grip once, he then promptly and properly threw that away as recoil was unpleasant, and the ability to shoot accurately was all but impossible. This fellow by the way is a big boy, about 6'8" and he is not easily intimidated.
A common failing of all of the Mossberg guns equipped with synthetic stocks is that the length of pull is too long for most people. With plastic furniture this is not as simple a fix as it would be with a wood stock. I've never bothered to cut mine down as I have a speed feed stock and do not wish to loose the usefulness of that feature. Probably I would be better of with the gun fitting properly as it carries lots of ammo even without the speed feed feature, what with the long magazine and a Side Saddle. Undoubtedly it costs me some time when I need to shoulder the piece quickly. The stock length of the 500 and the Maverick seem to be even longer, and the guns must be pushed well out in front before they can be brought back to the shoulder. Add to this bulky outdoor clothing and the situation does not improve.
My suggestion therefore, is to get a Mossberg 590 and have the length of pull addressed should it need to be. A side saddle is useful, although the additional ammunition does add weight to the gun. An advantage of the Side Saddle, beyond the additional rounds, is that it replaces the trigger group retaining pin with a hex head screw. A word about the speed feed stock should you go that route is that the springs behind the plungers are right against the rubber of the recoil pad. I did not care for this as the back side of the pad was becoming damaged, so I found a thin piece of stainless steel and used that as a backing to protect the pad. I wrap electrical tape around the gap between the butt and the pad and this keeps out moisture and debris. The 590's sling swivel arrangement is very good, but I found it useful to Lock-Tite in the front swivel to prevent it from turning. When you purchase your gun (what ever that gun ends up being) ensure 100% reliability before you decide to stake your life on it. If it fails to feed, fails to eject, or fails to fire, it is not suitable for the task you intend to use it for.