Last year the caribou hunting on the Great Northern Peninsula was pretty tough. (Its actually been pretty tough everywhere on the island, as the woodland caribou population is taking a nose dive in recent years due to a number of factors, including increased predation (coyotes and black bears principally), loss of habitat, and disease). That said, an outfitter on the GNP is probably going to be taking you into the back country, and you're considerably more likely to find a nice stag where the locals can't typically access.
Its hard for me to say whether its worth the money to you. I can only comment on the availability of game. I'd say if you ever want to hunt our woodland caribou, you'd better do it now rather than later. It may not be an option later.