I've been shopping for old computer crap on eBay lately (for nostalgia rather than collectibility), and I suspect your 1983 NIB Atari 5200 trackball would bring ten, maybe fifteen bucks (but I haven't been shopping for Atari game gear, so I'm really guessing). If ten or fifteen bucks, and reclaiming the space it takes up in your house, is worth more than the trackball to you, you should sell it. Part of the fun of these old machines and things is that they are dramatically cheaper than when we were kids. We couldn't have every cool peripheral and game back then, because it would have been cost prohibitive. Today, with stuff going for tens of dollars, even things that were very expensive back then, we can pick up just about anything we like and satisfy those old lingering curiosities. And, then, when we get bored with it...pass it on to someone else at about the same low price.