I've recently got back into retro gaming, having somewhat tired of the cost and constant updates to modern titles, and looked into picking up a Vectrex because I never had one as a kid: working examples are now going for £900+ in the UK so I dropped the idea.
EDIT: Having said that, I just checked eBay again, and it seems like availability is up and prices are down. A bunch of auctions under £100, and some Buy It Nows for around £200. Hmm.
Our (richer) cousins got bored of their vextrex, so it passed to my siblings and I. At the time I thought it was near magical, not needing to take over the family-television, or load games from cassette.
I still remember the fun of playing games with the wrong overlay placed over the screen. For those who don't know the vextrex used vector graphics, only in white, and alongside the cartridges each game contained a transparent piece of plastic with colours, score-labels, etc, which you placed over the screen.
The wikipedia article has a couple of brief pictures that make this more clear than my early-morning words could:
