Sanity and The Accumulation of Stuff

All through my homeschooling years until just recently, I have been acquisitive. Not a big spender; not generally buying at regular price, but at every opportunity I added books and resources to my library. Our house is now stuffed and overstuffed with homeschooling supplies; if we had lots of kids, it would be justifiable, or even if I still had one who was passionate about reading. We have two kids, though, and one is 23 and not only graduated homeschooling, she's graduated college, and I'm down to one. Our son is 13 and is really just not crazy about reading. All these books are at our fingertips, but instead of saving us trips to the library they create the work of reevaluating, sorting, cleaning. Because it has dawned on me that most of them are now either under my one pupil's learning level, and much of the rest of it is either oriented toward our daughter or has the ongoing drawback of being the written word, I have gone through them and have a nightmarish quantity to get rid of. 
I know there are others who can use them; I bought educational and interesting materials, not fluff, not junk. I know I can get rid of them. No one ever told me just how much more difficult it is to drag things out of a house than to drag them in! A strange and overwhelming lethargy and confusion overwhelms me at the thought of it. I don't want to "dispose" of them so much as to make my money back out of them. It would be great if selling them provided funds to buy my son the French horn he wants to start playing next year.
So I've been exploring options. I asked friends if their homeschooling groups are having curriculum sales; none seemed to be planning any. It almost made me want to stomp; I never belonged to a group that didn't do that at the end of the year! Okay, so what next? I have to evaluate which will be best: Craig's List, Amazon.com, eBay, or a homeschooling garage sale. And then what to charge? I looked on Amazon at what each book would cost including shipping, and wondered if 75% of that would be a fair price in a garage sale. I'm still working on it (though I've refused to look at it for about a week); I'm still a bit overwhelmed. 
If there was anything I've been learning from this, it's that I shouldn't have bought books I could get at the library. I should have carefully evaluated what we could use in a year and not bought "just in case," and just because it had merit. I wish someone had been warning me! I should have gotten rid of some of this stuff a few years back, a little each year along the way, and I wouldn't have such a big job now. So now I say to you who are just starting out and easily charmed by everything homeschool: Be careful what you drag home, and how long you keep it. Someday it's not going to look so charming and so useful, your 50th time of dusting it off.