if budget and running costs are your main concern,
then don't bother looking at anything other than a R22.
With a turbine, you are supposed to pay the full duty on Avtur for private use. The law came in about 12 months ago now.
This pushes the price of a litre of Avtur up to about £1.20, plus VAT.
Whether you declare your flight to be a business flight (and therefore qualify for the much lower price of Avtur) is another thing, of course.
As for other piston helicopters, anything and everything will be more expensive than a R22. A R44 wil cost you approximately double what a R22 costs you to own and run.
And if the mission is hours building, you don't need to get anywhere quickly!
It's not just fuel burn - you have to factor in maintenance costs and purchase and re-sale values.
You'll pick up a Enstrom 28 for less than 30 grand, but I suggest you ask any maintenance outfit that services all types of light helicopters and see what they say about the maintenance costs of a "cheap" Enstrom.
hope this helps,
Big Ls.