Since when was $700 reasonable for a game?
Well, first of all, your own formula (50 mo x 15 + 50 x 2) comes out to $850. In the interest of full disclosure, the original game was $50 and the two expansions were $40, so add in another $30, and you get a cost of $880 for playing WoW since release and paying by the month. If the average game is $60 and provides 10-20 hours of gameplay, that's $3-6 per hour. If you've been playing WoW for 50 months at a cost of $880, that's $17.60/month. If you play 5 hours and 52 minutes per month, your price per hour is $3, the low end of the price per hour of the average $60 game. So to answer your question, yeah, it's probably an unreasonable cost if you're playing much less than 6 hours a month, but how many people paying for the game since release actually play that little?
Kleeneness is next to Godelness.