Boats get more expensive not so much by the foot but when you cross the line for equipment size. Meaning, do both boats use the same engine and shaft size? If they do then they will have similar operation costs. If the 44 uses two small Cummins engines with a 1” shaft and the 48 uses two big CAT motors with 2.5” shafts, well now you are going to see a big difference in operation costs. If the 44 has good layout but there just isn’t the room for accessories like watermaker, Air condition, etc. and the 48 has the room for these accessories, well expect an increase in operation costs.
So it’s hard to tell you if the two boats are comparable or not. It just depends if you crossed the equipment size line.