At the moment it should be possible to get it for around 0.70 euro/litre....ie 5600 euro for 8000 litres (or maybe even less).
Not necessarily. If its (for example, an EC135) sat on a yacht then its generally non commercial operations so higher taxes. Fuel taxes as you are aware vary by country and it depends upon where the vessel was bunkered as to the VAT and MOT eligible.
A lot of helo's sat on superyachts are obviously private operators even although the aircraft may be under management by an AOC holder, the operator cannot claim tax free in many cases as it is a private flight. These days, many of them are M-registered meaning private flights only. Where I'm based, private flights pay around 45 cents more than commercial flights per litre.
The fuel supplier is also transporting bulk fuel to the yacht in a bowser, adding to the cost.