A it old, but seems in OK shape -- Sunlight hard-side campers brand new then were only about $7500 - $8000 ... So this one is higher price than I'd think was a good deal.
Like mentioned above, once you hit the $5000 mark you can get a lot more for the money, and even at your $3500 can get a nice HS with full bath if you look around a bit. You might be good at $2500, if it's only the heater that doesn't work. Sunlight is also a 'low-end' entry level product at its build value.
Once something breaks tho, and an owner doesn't care enough to repair it, then it tells me other maintenance has been skipped too. So, that's not a good sign to me at least. I'd certainly inspect it very carefully and check all the systems ... look for leaks and water stains - soft spots.
Eve when we find a 'deal' -- once you put $1000 in repairs, it's not a deal anymore, and at the very least, you need a new heater.