I am flying from Vancouver,Canada to Puerto Vallarta Mexico in February and am going US Airways to Phoenix,short stop over,then on to Mexico, what should I know/do to assure I will be able to take my Cpap on the flite with me?

I have been checking the internet for a new machine as mine is already 7yrs old and I would like a new one,but, looking at the prices for a new machine is very expensive in Canada,yet, in the U.S. it's almost 1/2 the price for the same machine,can some one tell me why that is? Also,does anyone know ...