Hawkesy:
It can be difficult, but it can also be a success. You need to plan on 500 hours a year to be viable (that is, make a profit), which is ten a week. There is staff training to be included (PPCs, recurrency, first aid), and I reckon that a husband and wife team who owned the helicopter outright and kept good control of the costs could make a living, if they had a market and, if they hired any staff, ensured they were well trained.
Two tips: make sure you get a reliable machine (206) and that you give discounts after people have done any flying - I used to have a lot of people come in the office and say they wanted to give me lots of flying and how about a discount, so I said yeah - every 10th hour free, or whatever.
Actually, 3 tips: You need to be able to pay for everything up front. Paying as you go along on anything more than about a third of the investment will kill it stone dead.
I just did an article on this in one of the helicopter magazines (not an American one), but feel free to PM if you have any questions.
And starflexes (AS 350/55) very rarely use up their full hours allowance - more like two thirds before you have to change them.
Phil