Olly for 50hrs a year honestly don't bother. Insurance alone if insured for 'club' use (required for training) is going to be around £15k for a newish R44, thats £300/hr at 50hrs/year, add fuel, scheduled maintenance, unscheduled maintenance, hangarage, depreciation etc and you'd be paying far more than the rental costs and you take on a lot more hassle. I used to own one. Even after leasing to a busy school it will not make a profit or cover it's costs. I found that my machine made a cash loss of around £2k/month when factoring in servicing, insurance and rental income. Thats before depreciation and my own cost of fuel for private usage.
You'd be much better off joining a private syndicate and splitting those costs between 3-5 people for the perceived usage your talking about.