I am enjoying this game immensely and haven't paid a penny yet.
If I did, it would be $5 for 2 more character slots.
However, this synopsis makes it clear what is coming down the road
Neverwinter's F2P Model: What you need to know
I'd recommend Neverwinter Online as a fun finite leveled game (up to level 60) .
But for those who crave PvP and end game content, its going to cost.