What is your suggestion?: Reducing price for ammo mould (Maybe just 1k slayer points? Up the cannon pieces in price to balance the change) or moving/adding it to a different shop such as the achievement diary shop, vote shop, daily rewards shop etc.
Is this in OSRS?: Yes, but you can buy it for 5gp from the dwarf after the quest.
Has this suggestion been accepted already?: No.
How would this benefit Alora?: Well considering you can already obtain 100's to 1000's of cannonballs from various monsters in Alora already, why should it be 7.5k slayer points? Also it would benefit for the daily tasks, which most players won't be able to complete today.