In Tucson, a used book store called Bookman's pays you for some books & magazines and resells them. QNM is one of them. I save mine, so I don't know how much they buy them for, but others in Tucson who want to find OLD issues can look there.
Saving to a portable hard drive is a great idea. I use binders now - but I have a lot of them. I'll never use all those ideas in my lifetime, but I keep saving them anyway!