Not really. You are assuming that prices go up at a constant rate and that there is a linear relationship between boat size and mast
size. Neither of these is true, or even roughly true.
For a particular extrusion price
goes up as a function of length, but even here there are certain plateaus. For instance anything under 40' can be shipped LTL in a singe container and won't need sleaving. Anything between 40' and around 45' can go in a single
container without sleaving. There is a major difference in LTL freight and full container freight costs.
Above 40' you get into other issues. Between 40-80' a mast
only needs to be sleaved once, so they all have the same shipping
and handeling costs regardless of leingth, but over 80' would need to be sleaved twice (though in reality a mast this big is likely carbon and everything changes again).
Mast design also can radically effect prices. So a 40' heavily tapered mast will be much more expensive than a 40' continuious extrusion. And a multi spreader rig allows a smaller tube, but obviously has more bits that need to go together and thus more labor.
As for boat size... Again it really depends. Like with boat leingth there are plateaus in mast height. A lot of boats that ideally may be designed with a 54' mast for instance may come with 52' because of bridge height issues, or because of shipping
concerns, or because a designer
wants to intentionally under canvas
the boat. Cruising boats for instance almost always have shorter masts than the same boat intended for racing
, just to expand the wind
range the boat is safe in.
Frankly you have a lot of moving targets, and a simple formula that doesn't take them into account won't give you a very reliable guess at cost.