The SKS is a perfectly acceptable hunting rifle, and they can still be bought pretty commonly for under or at $350.00.
I would agree absolutely that they are not the perfect rifle, and it is true that one can buy used a perfectly acceptable hunting rifle at or around that $350 mark. If I was in that situation knowing what I know now, and I wanted a hunting rifle, I probably wouldn't pick an SKS.
However, as a few others have said, a good SKS can be so much more than just a hunting rifle. Hunting, defense, plinking, solid truck gun, or even just blasting away for fun. I don't know many rifles that are as cheap even at todays prices (and again, $350.00 is my max price) that are also as versatile and as fun to shoot.
And that, friends, is the key to me when it comes to the SKS: They are fun to shoot. Look through this thread and there are a number of people who say "the SKS was my first rifle" or some variation thereof. How many people got into hunting and shooting because of the SKS? I don't have any proof of the following statement, but I think for a certain generation of shooters, that SKS was one of the top (if not the top) choices for a whole lot of people when they got into centerfire rifles or even rifles, period. I mean, they don't beat you up, they were super cheap and plentiful, they aren't hard to shoot with relatively good accuracy (though I am not claiming they are super accurate rifles by any means), and ammo was and still is cheap so that means they got (and still get) shot a lot.
So, yeah, to a certain extent I do think they are underrated. They are judged sort of unfairly by what they can't do, as opposed to what they have done. They are not the perfect rifle, but boy, they are pretty far off from being the worst choice! And, speaking of choices, I will tell you the truth, as much of a Ruger fan as I am, I would choose an SKS exactly 100% of the time over a Mini-14/30 for a utility/truck rifle.
With all that being said, when it comes to milsurps I have always wanted to take a Mosin hunting. I love, love, love Mosins. I have other and better milsurps, and definitely better production hunting rifles, but there is just something about a Mosin that trips my trigger. I regret not taking my Mosin with me on my hog hunt a couple of years back. Next time I go, it is going with me.