Harry O - not quite sure if you're typing tongue-in-cheek, or how familiar you are with 135 maintenance intervals, but all the NPAS machines should now have migrated to the 500/1000hr servicing intervals, unlike the 902s which require 100/200/300/400/500/600/800hr servicing, as well as a long annual!
The 135s have a few minor checks on ancilliary equipment, but they're easily completed at the bases, in a few hours in most cases, minimising downtime.
Not quite sure where you get the "
902 long maintenance services" from. Unfortunately, probably due to the numbers in circulation, there's been little interest/money to initiate the type of maintenance reduction programmes that ECD/Airbus have done such a good job with over the last 10-15 years.
Can't speak for the 145, which is hampered by the vintage of the drive-train, I understand, and therefore requires a more exhaustive maintenance regime than it's little, but younger, brother.
Costs? You'd have to ask elsewhere.