Ditto what @johnpowell said. I’ve used zen cart and made it work the way I wanted it to, but it’s a lot of work and pretty complicated – if you were setting up a store that you were going to continue running, I might recommend it – but for something short-term like this, it’s really not worth the time.
If you really want to avoid eBay, Craigslist is a good option (if you live somewhere that Craigslist is popular). If you go with that or a garage sale, you won’t have to deal with shipping either – people will come pick things up from you themselves (always a plus when selling a lot of stuff!)