Depending on where your house is - the average rebuild cost varies - Dublin was traditionally dearer than the West.
A rough guide in todays market would be 100 Euro's per square foot or 1100 per m2.
Alot of people were 'duped' into believing that if theypaid 400,000 for it then they should insure it for that !, without realising that the purchase cost includes other 'big' items like Site Cost, and closeness to servises - all of which your insurance co will have little regard for if your claiming.
I recently rang the AA for a quote and like you they couldn't quote for less than 250,000 so it seems they like to keep that as a minimum amount.
Anyway Allianz were much cheaper for increasd contents cover.