I am advised by the Revenue Commissioners that the most recent estimate for reverting the reduced 9% VAT rate back to 13.5% is that it would result in extra revenue in the region of €491 million.
A pre-Budget 2018 Ready Reckoner is available on the Revenue Commissioners website at: http://www.revenue.ie/en/corporate/information-about-revenue/statistics/ready-reckoner/index.aspx.
On page 26, this Ready Reckoner shows the impact of a 1% increase in the 9% rate to be €109 million, which can be multiplied on a straight-line or pro rate basis to calculate the effect of increasing the 9% rate to 10%, 11%, 12% and 13%.