Its actually just a utilization problem. I would not classify your operation as a commercial op. What you use in a year would be what most of the caravan operators would do in two weeks.
For arguments sake, the 4 yearly inspection is $13,000.
$13,000 / 200hrs is $65 an hour.
A typical operation is around 1000-1200hrs a year. Using 1000hrs. $13,000/4000 = $3.25 an hour.
Even if it wasn't calendar requirements and just a $34,000 bill.
$34,000 / 50hrs = $680 an hour.
$34,000 / 1000 = $34 an hour. Hardly a bank breaker that makes the caravan uneconomical.
It makes a huge difference in running costs.
With your utilization, any aircraft with calendar items is going to be a huge cost per hour.
While the scheduled stuff costs a little more on the van, the dispatch reliability is hard to beat. The unscheduled maintenance on the PA31 is getting higher as it gets older.
I've operated both machines. The caravan beats the PA31 hands down in nearly all aspects.