Getting a rough idea of viability is not that difficult. First thing to understand is that the cost of increasing benefits rises exponentially and the real issue is where you want to draw your own line.
You need to be clear where you want to travel to and from. For helicopter to be the logical choice, subject to cost, it needs to be much the quickest. That means (a) you must be able to take off and land at (or within a few miles of) the sites you want to use, (b) small/medium airfields are some distance away, and (c) distance is not excessive for heli's relatively slow speed; eg more than say 200 miles.
Let's assume it's a yes so far. The starting point would be a say £100k Robinson R22 with just 2 seats, but that is highly unlikely to be practical unless it is only necessary to take one pax with a folding briefcase, in daylight in good weather.
So you need to think about how many are travelling. Chances are though it is just 1/2/3 pax - in business, few trips need to be more than this. Will it be expected to carry normal luggage? If not, and you want to transport up to 3 people with minimal luggage, then consider a £150k - £300k Robinson 44 or Hughes 500. If you do need luggage space, and this is normally the case, you can rule these out and turn your thoughts to a Bell Jet Ranger (206) (4/5 seats), Eurocopter EC120 (4/5 seats) or single Squirrel, AS350, (5/6 seats). Price bracket now starts at £250k for a reasonable 206, through £350k for an older AS350, £500k for newish EC120 and up to £1m for newish AS350.
This is probably the area you will need to consider closely and where most biz heli ops start. Assume running costs, excluding (i) interest on capital (ii) (modest) depreciation, (iii) pilot, of £60k - £100k per year, based on typical 250 hours usage. Total realistic annual running cost - probably around £150 - £200k.
Now for the majority of your requirements this will do fine, but everyone, particularly the pax, will need to understand that say 5 - 20% of trips will be delayed or cancelled because of poor weather - low cloud mainly. Flying at night also adds significant risks and is probably also a no-no.
To reduce the chances of delays/cancellations and fly happily at night you need an IFR twin, and the Twin Squirrel AS355 (5/6 place) or Agusta 109 (6/7 place) are your next options. Prices from £500k for an older AS355 or A109 through £1m - £1.5 for a newish AS355 to £2m for a similar A109. Twins are also generally required to be permitted to land in congested areas, like towns.
Assume running costs, again excluding (i) interest on capital (ii) (modest) depreciation, (iii) pilot, of £100k - £150k per year, based on typical 250 hours usage. Total realistic annual running cost - probably around £300k.
So you pay a lot more for an IFR twin, but you do also get the highest levels of safety, for a variety of reasons, and many are prepared to pay a lot for this and indeed some executives insist on twin only. There is also the issue of perceived safety.
Now at this point, having kind of assumed that one could get IFR twin capability for £100k per year, most interest fades away, at least until the business case builds again and the costs are accepted - proving justification is difficult.
I should stress all the above numbers are off the top of my head, but should be ball park enough to decide what you want to do, and not waste a lot of everyone's time looking at the detail, which is only necessary once the company is pretty sure it wants to go ahead, in order to choose the right specific aircraft. There is a huge amount to consider and using a well respected heli consultant will be money well spent.
Rental is certainly a good way to evaulate operational viability and for many is the most sensible way forward anyway, but it does depend on having a suitable operator and heli reasonably close by, otherwise positioning costs add up quickly and may well mean that you are paying for say 50% more hours flying than you are actually travelling in.
There is also the potential of lease-back on some aircraft, but again get careful advice on this. Certain aircraft, eg B206, A355 are much better for this than others.
I'm sure there will be many other views on all of this but hope this info is of some use to anyone considering the big picture of the viability of a company helicopter.
Let us know what you end up deciding!