2 or 3 days use, 6-8 times per year?
You don't want an aircraft, you want an operator who has an aircraft otherwise your expensive asset is going to sit on the ground (costing money) for 341 days per year.
Therefore I would start with the data you give plus where you want the transport to / from and that allows you to factor in the additional cost of relocating a machine from wherever it is based, which you would have to pay in addition to the hourly cost for machine / pilot.
4 pax = R44 or EC120 or Jet Ranger territory. Cheaper to operate than flying with empty seats. This side of an A109, though, your pax are likely to need headphones so if you want unltra-refinement of being able to talk without the head gear you might be looking at an A109.
Is the impression that your pax get important? If so then an R44 looks a little less impressive than a Jet Ranger, and once inside an EC120 or EC130 looks a whole lot better and significantly more comfortable (newer design).
Why not look for an operator or two who have a range of aircraft and go pay them a visit. Seeing the machines in the flesh will give you a better idea and you can talk costs of operation.