oblib, i would not buy a house with a history of subsidence. yes your insurance premiums will be very high if you can get insurance at all in fact. my sister law in the UK had subsidence on her house about 5 years ago, did an insurance claim, had the work done etc, house all ok but she tried to sell 2 years ago and as soon as subsidence was mentioned potential purchasers walked away. she has approached a few agents and they said they will struggle to get her the market value and she may have to take a massive reduction even though the house is perfect.
with all the houses for sale in Ireland, why buy one with subsidence. this ia a major investment on your part, so why risk losing money.
anyway, you should have been informed much earlier in the sale of this problem. why dont you phone a couple of insurance companies for a quote?