I just bought one at 4videoequipment.com for like $800. It was a 1.6. Works great, took some hassle to get it but itsa niccce. IT was for the DVX 100 but I believe they are interchanglable.
Whatever you do, don't get one off of ebay. Century Optics is the way to go, here. You pay for it, but the cheap knock offs don't work and they make your footage look like crap.
I'm not sure how to measure this, but how much closer does 1.6x get you? Does anyone have screenshots to compare the on board lens to the 1.6x telephoto lens?