Originally Posted by
Soukyuu
The price is set by the community, so changing it to another materia won't work. Even increasing the conversion chance won't work.
The reason some materia is cheaper than the other is not necessarily the attributes it grants but which class is most likely to use it. The reason Manathirst is priced so cheap is because it's for MNK's relic and otherwise pretty much useless. While Heaven's Eye is for a tanking/buffing class that is much more welcome to your typical endgame party.
Which means people will put it up for a higher price because it's more likely to get bought for this price. Who'd buy Manathirst IV for a few mil? Heaven's Eye seems to be selling nicely and growing in price.
Bottom line: if you don't like the prices, don't buy. The price will regulate itself down eventually.