Hi Pam!
Glad to hear you'll be here soon.
If you buy your train ticket in advance you can save money and you can do it from
this page of the Irish Rail official website.
Just click on "Plan Your Journey" to see timetables and costs and book your ticket.
To get to Blarney Castle from Cork you can also take a bus, Bus Eireann - line 215. 🚌
Otherwise you can take a taxi like you said.
Here you will find all the taxis you can get from Cork.
I hope this information helps you and if you have any other questions don't hesitate to ask! 😄