Sovereigns have always held a very high price use, especially the ELite or GT these days, but I see that Minelab has lowered the price of a new GT a good bit, probably to clear out stock with it being discontinued. I'd expect though, that when the new stock dries up, the used price will climb even higher than the already premium used price they seem to go for. Good reason why even the older Sovereigns long before the Elite even sell for a decent buck these days, and that they aren't exactly easy to come by in how often you see one up for sale. Man, I have a eight inch (actually 7.25" in true size) Tornado on the way as my super heavy trash coil as I hear good things about it's depth and separation compared to typical 8 or 9" true size coils, and that pic you posted of the little guy next to the 10" Tornado really has me excited to get mine in lay away paid off and mailed to me.
With the aftermarket shaft and such, I bet if you had a meter with it you would have got that price, especially with both Tornados. In fact, I'm surprised it didn't sell at the first price even without the meter, but maybe the price reduction on new units is pushing prices lower a bit right now on used ones? Once the new stock dries up though I'd expect prices to go through the roof on used units, just like I expect the same for the SE Pro.