76 suns won't go for higher than 1bill atm, unless they are +9 fb and ****... 2h suns... Forget about it, you probably won't have enough gold for it, or money for the gold. I can only tell you it goes for way higher than 5bill gold.
Prices vary from server to server, but if you can afford to buy a sun for 7-8bill, you can afford to buy a sun for 9bill, soo it's not really that much.
iris is dead lol, i used to play on iris, there is only like a few lvl 76 sos and even fewer som , and like 10 suns in iris. iris is a dead server based on items, so it has a total failure economy. id say it probably go higher than 3-4b
