NEVER book your airfare with a package at WDW. The cancelation terms are aweful, and the fares aren't very good.
I have to disagree with the above posters. I think January is WAY too early for aflight for December. Now is too late to get the best deals (for this December), but January is a bit too early.
It especially matters if there is a discount carrier flying out of your local airport. If you aren't sure, then I would suggest finding out for sure. Southwest is expanding all the time, as are the other discount carriers. Also, I know Montana is a big state, I don't know if you have any options for airports. Sometimes driving a little further for another airport can make a big difference in price. I have a few to choose from where I live, so I usually shop around. Especially factor in the idea of a different airport if you are unable to get a direct flight to Orlando from your area.
If, as you think, there are no discount carriers in your area, then buying relatively early is a good idea, but I still think January is way too early. They aren't going to offer anything remotely resembling a discount THAT early out. My rule of thumb for my area is to look about four- 4 1/2 months out, and keep checking. With Southwest, if a lower fare comes out, you can rebook your ticket, but I know many major airlines charge you a penalty for doing that. In my area, when Sothwest releases their sale prices, the other carriers magically discount thier fares as well (and this is the case for other discount carriers too. When they release their lowest fare, other airlines will match).
It also makes a difference if you plan on flying Christmas week or earlier in December. Christmas week buy early, other weeks, it would make sense t o wait longer, especially if you have some flexiblity on when you fly.