Re: 50 Liter pack for 3 night solo trip

There are a number of sources for used gear--the obvious one is eBay,but there are others online as well. There is a used gear forum here, The Lightweight Backpacker has one and I've seen others on various trail and hiking sites. Also, I've heard of some good finds at local second hand stores--depends on where you live, I suppose. You might look at Secondascent.com's website. They are in Seattle but not sure if they do mail order. They offer some discounted new gear. I just heard about them, don't know anything about them other than the website.
I've bought a few used things-tents, pack, down jacket, so it's just a matter of lots of looking and asking questions.