We are flying Alaska airlines in a few days it is $20.00 a bag then if it weighs over 50 pounds thats an extra $75.00 . My wife managed to get all of our stuff in one big bag and to carry ons
It's generally a lot less expensive to take two suitcases of medium size than to take one big suitcase that's invariably overweight when it's full.
Two medium suitcase that weighs five pounds can take 45 pounds of contents -- each -- without violating the weight limit, but the suitcase twice as big (in volume) that weighs ten pounds will go over the weight limit when you put 40 pounds of stuff into it. The medium suitcases probably are small enough so you won't be able to cram more than thirty pounds of stuff into each of them, but the big suitcase will take it all.