> Blizzard did not charge for WoW Classic. It merely requires an active subscription to the regular game. There's no additional purchase or subscription.

I'm not sure what you're getting at, in my experience a massive chunk of the players don't play 'retail'. So the cost is just that, $15 a month.

Beyond that, do you have a source? It's not clear that any of these things they've been developing had significant costs in replicating for Classic.