You might do a search for trip reports from Christmas time in previous years.
That might give you a good first hand perspective.
In re-reading my previous post, I sounded quite negative. There are lots of people who absolutely LOVE going at Christmas. The decorations are incredible and you've got Mickey's Christmas Party and the Candlelight Procession going on.
You will have a good time if you keep your expectations reasonable. There will be long lines for everything. Some you can alleviate with careful use of FastPass; others, like lines to check out in a shop, or in a restaurant, cannot be avoided as easily.
There are many strategies for dealing with large crowds--early entry, E-nights, FastPass, eating at non-peak times, getting PS for your "must do" restaurants, using a tour plan.
There are also ways to keep your costs low--eating major meals off-site, taking snacks into the parks, staying off-site, keeping breakfast or sandwich stuff in your room, etc.
It CAN be done.
Good luck making a decision.