Hi colm5
If you can get an attic done for 350-450 euro there must be something wrong, under building regulations and best practice they have to build a walkway to any serviceable area like a water tank or a HRVS, this should include hand rails, also they must install eaves ventilator trays so as not to ventilate through the insulation, I would think anything below 1,000 euros means it's not being brought up to standard, look into the requirements for contractors on the SEI web site under the scheme.