As I've said many times, with most equipment, the price can vary greatly with the amount of storage space available to the seller.
With older technology exposure units, you obviously have a new factor as well.
In general, for buying, I have always shot for 60% of new for mildly used stuff.
With the obvious new development in this particular field of equipment, I'd have to say that if you want to move it sooner than later, drop it significantly further than that.