First off that valuation on the ROS web site seems to be very high considering that the Antara has a starting price of just over €40,000 here, but I can only think that the valuation is based on the higer spec option which has a retail price of around €53,000. However, there are a few key things you have to keep in mind:-
Trim level: The UK use a different trim level to us so you need to value the UK car on as near a trim level as possible to here to get a true value for the car. If the Antara you are looking at is automatic then the value is higher again. The trim level has an influence on value and any added extras can (and sometimes will) be added to the OMSP that the revenue have on the web site. You can dispute the value on the site with your local VRO if you think the value on the web site is too high. You may need proof that the car is being sold in Ireland for less than they are stating but you need to find an identical car here with similar trim level and mileage. Maybe a print out from CARZONE.IE with similar cars might help your case.
C02 Emissions: All cars being brought into Ireland are charged VRT based on the cars emissions regardless of age (unless classic or vintage). The Antara has a C02 rating of 198g/km which is quite high and this gives a 32% VRT rating of the OMSP of the car. Even if you can get the VRO to drop the price to say €30,000, the VRT would still be around €9600.
Road Tax: For a car with a C02 level of 198g/km you are looking at an annual road tax bill of €1050. That could rise over the coming years as the Government increase the taxes to try and get their coffers back in order. However if the car was first registered in the UK between 1st Jan 2008 and the 30th June 2008 you will be able to pay the road tax based on the older engine cc system which at the moment would give you a road tax bill around €600+ per year.
Hope this info helps and doesn't confuse you even further.
P.S 4x4 vehicles will have a pretty high C02 rating so if you don't need the 4x4 option maybe a 2x4 vehicle might be a better "financial" option!!!!