Why should I pay for a pig in a poke?
Not sure exactly what you are looking for. Do you mean prices on items in game, so prices in terms of gems. Or do you mean prices in real currency?
The closed chest gives a list of all possible items to purchase and their main stats (not all stats are available for all items though.)
The chest with gems lists the possible amounts of gems you can purchase for real cash. Not sure where you go to get information about a subscription and what that gains for you other than to click on a level you don’t have access to.
I mean for what I should pay $6 per month?
The subscription modal (you get when you click on paid level) loosely covers that:
- extra levels
- extra characters (more importantly extra two character types — ranged and magical)
- 3500 crystals/month bonus
I would say at the moment it’s best for either exploring more character types and/or being competitive in multiplayer (3500 crystals make serious difference in equipment right now).