the deisal's are not that much money when compared to gas motor's the problem lie's with in the drive set up on a pre rigged gas motor with a bravo style drive . if you are buying a brand new boat and get the surface drive's from the beginning i don't think there will be that much off a cost difference .
i have been looking into buying a used boat and replacing gas motor's with deisal's ,the motor's are not that much money it's the dam drive's that cost almost as much as the deisal motor's
FPT 560 hp 1300+ lbs tQ = $ 33,000 and change x 2 == $ 66k
# 8 surface drive's and transmission's x 2 = $ 65k
plus the re rig .
now some 525's will cost the same amount new the differences is u don't have to replace the drive's .
so when buying a brand new 38 to say 45 footer and your spending $250+k the $ 10 k to $20 + for the unbreakable drive's is not that big of a deal but to sink say $ 130 k into a used boat is a lot of $$$ .
just my thought's