7 billion is the highest I've seen a lvl 90 +15 weapon go for. 5 Billion is the lowest I've seen one go for. This was back when oj weapon prints went for 200mil. So for 200mil, and maybe 2mil for secondary purples, you could craft a lvl 90 weapon and gamble it with fergus. If you break that down to the highest and lowest +15 buys, that I know of, it comes out to 35 to 47 weapons crafted at a 200mil price point per piece.
If you read this far, you're probably wondering why it matters. It matters because now you can make the same purple oj prim weapon for basically free. Completely free if you use seals for all the mats. 1 to 2 mil a piece, if you buy purple secondaries. Lets keep this though around gold. Oj weapon prints are now 25 to 50mil on the mp, depending on the weapon print name. A 200Mil oj weapon print times 35 is 7 billion. A 50Mil oj weapon print times 35 is 1.75 billion.
I'm not saying +15 lvl 90 weapons will now cost 1.75 billion, but I am making a prediction that +15 lvl 90s will average 2 to 3 billion in 6 months; if prices remain consistent as they are now. There should also be a bigger surge in +15 lvl 90s in 6 months. +15s are still rare and there are still players with massive stores of gold, so it'll still be high currently, but gradually the price will decline over the months.
Onto the Mysterious Shard. For those that don't know, Mysterious Shard is the new Royal Raid drop that is used to increase the att limit of lvl 90 weapons. You need 120 of these to cap out on it, and the damage gained from it is immense. Currently some players are having trouble selling it, since they are getting lowball offers of 20 to 30mil. This stat/mat is the new endgame for those with +15 lvl 90 weapons. This mat should be priced at atleast 100mil, given it's rarity. Lets say though that players are selling these for 20 to 50 mil. 20 times 120 is 2.4 billion, and 50 times 120 is 6 billion. At 100mil a piece, it'll be 12 billion. 120 Mysterious Shards will be greater than or equal to +15 lvl 90 weapon prices.
I used 20mil and 50mil as examples, I highly doubt players will sell it for that much. Especially since these are royal raids we are talking about that host 16 players max now. Back when Blue tears were 400mil a piece in 24 man, how many of those did you see? Imagine trying to even collect 120 Blue tears back then, and that was with 8 more players per raid max with 3 to 4 runs per day. We have 8 less max players per run, 2 to 3 less runs per day, a much harder raid given the daily raid pick, higher chance to fail or quit a raid, and a much lower player base from the numbers in the Blue tear days.
Point is these Mysterious Shards will not sell cheap, if players are smart.
TLDR;: I predict in 6 months that +15 lvl 90s will range between 2 and 3 billion. 120 Mysterious Shards should exceed the price of +15 lvl 90 weapons greatly.
Other predictions for +15 lvl 90 weapon prices in 6 months:
20% max reduction. Using the base numbers, it'll be 4 billion to 5.6 billion for +15 lvl 90 weapons in 6 months.