Hi SEL
Where are you based? This will effect the cost's.
I have mainly experiance on the R22 and a little on the 300.
In my experiance the R22's are quite good on unsheduled maintance, As for the 300 I have to say the two I have flown didn't seem to have to many problem's either.
I am at our maintance company tommorow, They keep very detailed operating costs for each machine they maintain (Robinson only, Based on actual cost's not extimated)
I will ask (This will be in euro's and for a R22 based in Belgium)
If your looking at buying a new or used machine and your based in Europe then PM me.