It was 10 Gold which roughly translates to 15~20 PDs during summer event, as time elapse after event its price may rise until it was distributed in events again. There's probably still Gold leftover from event which would tie it to gold prices. Also there are leftovers from older event like last Christmas, but I don't know how many are purchasable, with a lot of people who got it back then inactive.
I think it would be a good idea to try buying one in the trade section and check the response.