Go see your agent and get a estimate of the cost. For me it runs just shy of $400 every 6 months with State Farm. But I am 3 times your age and have 3 vehicle insured with same agent. The CTS4 insurance is on par with the GMC truck I have.
I have a loaded 2009 CTS4 in Blue Diamond and I love the car. I had a 2005 CTS also and traded it in on the 2009.
Here is a tease to get you pumped up....my 2009
a pic of CTS on the assembly line in Lansing, Michigan