Idea

And when you purchase an item to player's inventory or character's inventory, there will come with an information on what price did you pay to own this item, and for how long.

I think there is an interesting discussion to be had about if this is good idea or not. A consumable version of an item is still a different item and I personally feel should be internally modeled as such. Would be interested in hearing other opinions on this.

What I'm having trouble visualizing is how you see the setup for this working. Right now, you would define three items, each with a distinct price. The first two would be consumable, would have a specific expiration period (2 days and 6 days), and if you want to be nice to players, they would have the same usage period group, so that if you buy one, then immediately buy the other, you'd have an expiration time of 8 days out. The third item would have yet another price, and would have no expiration. That would make it easy to then check for the presence of the permanent item, and if it's not there, check for the other items, and their expiration times. How do you envision applying three distinct prices to a single ItemId? What prevents a hacked client from buying the permanent version of the ItemId for the 2 day price, since it's one item? What does the setup process for the item look like?