I have been in a very similar position to you, I bought a refurbished R22 and used it to complete my PPL and at the same time leased it back to the school who taught me to fly.
The REAL cost per hour is impossible to calculate in advance. The organisation who sold me the R22 told me one figure, the school who leased the machine estimated another and my own calculations gave a different amount.
I believed that by leasing the helicopter to the school they would burn lots of hours and therefore bring the insurance cost per hour down.
Insurance £7K per year / 350 hrs = £20.00 per hour as apposed to my 80hrs private use per year at £87.50 per hour. What I did not realise is that the maintenance bills would be so big. When using the machine for training it really got a hammering, all those hovering auto's, auto's to the ground, run on landings, new student's trying to pull 30" MP and hours of hovering at max power. Within six months of owning my R22 I had a 6.5K maintenance bill for unscheduled work.
I lost money on every hour the machine flew, I sold the machine to the school that leased it and got an R44, and I lease this machine to the same flying school and have had much more success. Most people who fly the 44 already have there PPL and either do there type rating on it or self fly hire. The hours are much lower per year but I have had no unscheduled maintenance in nearly two years.
Hope this helps
PM me if you want to know more figures.