Yeah private Vanilla servers are still very popular, that is why Blizzard decided to release Classic servers ( starting with patch 1.12)as naturally they want their piece of cake, as they saw that there is still huge demand for Classic Wow.
Regarding asking for money, all you have to do is to have active subscription and you have both retail and Classic WoW available.And if you dont want to pay WoW subscription with a real money, you can always pay with gold, and it is fairly easy to farm it in retail WoW.For the last 6 or 7 years i haven't spent 1 cent on WoW, all my gametime comes from ingame gold.
BTW, if someone plans to play Classic WoW and wants to reserve some cool name, you can already do it, since last night.You can only reserve 3 names though.
OK, about how much in game time do you need for the game to pay itself? I imagine this is farming items and selling them, but is this allowed in game or outside? I remember games like EVE online kinda allowed it in game but not sure about WoW.