It's way less than the initial cost. I just did a quick search on the Internet, and found prices which are approximately 15%-20% of the initial cost for an additional year SnS.
These are the SKUs I found:
Standard-Support:
- VS6-ESP-KIT-G-SSS-C (1 Year)
- VS6-ESP-KIT-3G-SSS-C (3 Years)
Production Support:
- VS6-ESP-KIT-P-SSS-C (1 Year)
- VS6-ESP-KIT-3P-SSS-C (3 Years)
Note that the prices for Standard vs. Production support do not differ much,.
André