Poor Southerner,
Parts are fewer and simpler, Just look at the drivetrain of a 300 vs an R22, look at the undercarrige of the 300 and note all those extra parts including shocks that need to be serviced. You have one extra main blade that has a limited life and a more complicated rotorhead with extra dampers and other lifed parts.
All these lifed parts have their hourly costs added up so when overhaul time comes the cash is sitting in the bank to replace those items.
Also the fact that there are many thousands of R22s out there probably means the sale of far more parts which in turn brings down production costs.