long term it must surely be very expensive running a robbo if it starts clocking the hours up quickly
It just doesn't work that way in practice.
The day-to-day costs of an R22/R44 are pretty minimal: 50/100/annual checks plus some extra checks here and there around 500 hours/1000 etc
On most Robinsons most parts will make it to the life limit - there are a few exceptions - blade erosion, aux fuel pumps on Raven II's, but compared to the maintenance of say a 206 (TT straps, anyone?) or many others, it's pretty cheap to run, and the more hours you fly, the standing costs get smaller and smaller - less annuals, insurance etc.
If you do 1,000 hours in an R22/R44 in a year, you're probably operating one of the most cost-effective helicopters around.
The rebuilds (which vary slightly, e.g. new tailcone only on the second) should be seen as a provision for each hour of flight and built into your low running costs.
Lafite