I'm very interested in this model for a few particular reasons. Firstly i own a Hyundai Elantra with a towing limit of 850kg and this camper would be perfect only weighing 560Kg tare.
Firstly, as you have said this is TARE weight ... hown many ppl will be going with you and what are their weights? eg. two ppl approx 150kg.s is starting to get close to your tare weight ... then add all of your camping gear. Don't be put off by this, I reckon the Elantra 'should' be able to pull it. If you can, definately take it for a test tow. I know from personal expereince that Daewoo's are crap at towing but Hyundai does seem to make a better vehicle.
I'm willing to spend up to 5grand for this one which includes an annexe. From what i've seen on the net larger ones go for 5grand so I think my offer would be rather generous for the camper.
I haven't seen the camper so it is a bit hard to judge ... I know the Jayco Swan's from the 80's go for about that. Can you find out how long it has been up for sale? If it's been up for sale for a while he might be prepared to accept a little less. But $5k with an annexe seems a fair price.
Maybe post the link to the camper.