The price reduction would stack.
Each of those is it’s own type of curse, and thus reduces the price accordingly.
However, you should note that the cursed item crafting rules state:
Drawbacks and Requirements: Drawbacks and requirements typically don’t reduce the cost of a cursed item in any way (and might increase it). Since the crafter of an intentionally cursed item is setting these requirements, it is expected that she does so with a particular agenda, such as choosing a requirement that doesn’t affect her very much but would make the item painful for her enemies to use should they steal it, or choosing a requirement that she wants someone to perform anyway and then offering the item as a gift.
That said, these curses typically affect the price when selling the cursed items to a merchant. The price may be reduced by 10% for minor drawbacks or requirements such as minimum skill ranks or the worship of a specific deity; by 30% for harmful or costly drawbacks or requirements such as an alignment change, ability damage, sacrificing wealth, or performing a quest to activate the item; or by 50% for severe drawbacks or requirements such as negative levels that cannot be removed or needing to routinely sacrifice sentient creatures to the item.
So a cursed belt of +2 strength would still cost the same to craft as a normal belt of +2 strength, despite selling to merchants for less.
Note that this doesn’t mean a merchant will sell you the item cheaper either, instead they may charge you full price, as it’s only reduced when selling to merchants.