Prices will vary depending on your agreement with MS and what plan you are on, eg Select aggreement, EA aggreement, Open Value, EAP etc etc.

Base price on NL without software assurance, at last check was $1793 per core, so that works out at a 1 off cost for 12 cores of $21516, but if you want to add things like software assurance into the mix the price will jump dramatically.

Also if the server is hosted co-lo your pretty much stuck with what the hosting provider says the cost is.

You would need to ask your vendor what the price includes as SA can be quite expensive. So if you dont need it, then dont buy it, but be warned that if you want to upgrade within the 3 years, say if SQL2012R2 or SQL version 12 comes out, you wont be able to as your licenses dont cover you and you will need to pay again for the newer licenses.