Buy elvolving ring 3 or not?

But I cant tell if the ring will go up or down in price and the 3rd ring is almost better than ring 1 and 2 together (4 all stat difference, dont care about the hp)

After looking in the FM in the other servers earlier, that's the cheapest you'll get. They're about 300m in El Nido.
Go ahead and buy it, it's worth it.
The only ring that cuts close (dark angelic blessing) is about 300~500m.