Jim, in order to qualify for International Book Rate, the item(s) must weigh a minimum of 3 kilos and a max of 5. And it's more expensive to send to the US than to Britain/Europe. AND - of course - the charges have taken an astronomical hike in a short space of time, well above any rate of inflation or cost-of-living increase.
#whatsnew

http://www.anpost.ie/AnPost/PostalRates/Sending+Books+Abroad.htm