Decided to give in and try, huh?
I use auctionsniper.com - one feature I particularly like is the ability to create a bid group, and tell it how many of the items in the group I want it to win. Then it just keeps bidding on the items for me until it wins one (or however many I said I want), and then cancels the rest. That way, I can pick a price that I want to pay that's a bit below what the item usually sells for, give it a list of all of that item on ebay, put them in the bid group, and let it just keep bidding until I luck out and get that one that goes for a bit cheaper than all the rest.
Given that I'm not bidding on Theremins, I'm not particularly afraid to let you in on this "secret" bidding method...
By the way, that was a good price on that Etherwave, but you might want to keep in mind that some people have opined that the new Etherwave standard model in current production fro Moog Music may have some improvements over the older Big Briar models (which is what I have, by the way), so if you don't get another great price, if the price difference between used and new isn't significant you might want to bite the bullet and buy a new one.
And, don't forget that you'll need to get it a stand (about $25) and an amp (about $100 - from experience I recommend against getting a cheap guitar amp, and the Moog amp is only $99 anyway).