Treyarch says that, people are relaxed over the price of the previous map packs, that due to that notion, they're probably going to go with the 1200MSP tag that they've used in the past.
Source: CVG
Additionally, they said:Treyarch has claimed that CoD fans have relaxed over its 1200MSP price for Black Ops Map Packs - as they offer "a lot of value".
"It's a little of getting used to it, but I think people see there's a lot of value in the map pack. All four of our MP maps are brand new - they're not rehashes from single-player, they're not old maps that people have seen before. They also get new gameplay mechanics with ziplines and destructible bridges and auto turrets."
Source: CVG