We'll see, but having the Lawbringer, Valkyrie, and Shugoki costing 500 means nothing, as they are base characters that simply were not included in the previous two betas. People have played them already, just at press events and other betas, etc etc. Now the Roman Centurion looking guy and the ninja? Nobody has played them, and they're probably still a work in progress. Using what we know about the current characters, and applying them to the new ones makes no sense, as simply comparing the game to R6's second season pass indicates that they like the model.
I also went and did some research on the model that RS6 used. The new characters ended up being about $5 a pop, if bought with real money. Although I don't want to say that's definitive, logic would dictate that it's probably going to be about the same in For Honor.
Again though, where did the devs say this about being able to play the DLC characters without buying them? I've been following this game for months, and have never once run into that statement. I could be wrong, but I feel that if it were true, it would greatly devalue the season pass. Which is already a net loss if the characters are $5...because that makes sense.
