I've just closed the program, but if you look at modern hovercrafts, there's a small cargo HC with a cost of (IIRC) 218,000 while the passenger version costs 21,800. Looks like a typo.
Can you recall which specific hovercraft were affected?
After investigating the issue since April:
https://github.com/jamespetts/simutrans-pak128.britain/blob/master/boats/bht-150.dat
BHT-150(Piece)
cost=17500000
BHC-BHT-150_400(Cool)
cost=175000000
https://github.com/jamespetts/simutrans-pak128.britain/blob/master/boats/bht-130.dat
BHT-130
cost=175000000
Apparently they've become cheaper since April, but still a zero missing (or one too many with the other two).
Thank you for the report - now fixed.