Boots are too heavy for hand luggage - you need to put them through with your suitcase and the weight will be added. Normally it would be an inclusive price with ski carriage.
In my experience the package type airlines will tell you there is a charge and try to get you to pay in advance, however, if you turn up with your boots in your boot bag they will put them in the hold and so far, for no extra charge. Not guaranteed tho. The budget airlines are a different matter