Found this but no prices;
Google says that it's selling the 32GB + Mobile Nexus 7 unlocked and you can buy it with either a AT&T or T-Mobile SIM card pre-installed and you'll be responsible for getting your own data plan through a carrier.
It's important to note that HSPA+ is not compatible with newer, faster 4G networks, and is really a 3.5G technology. Google says that the 32GB + Mobile Nexus 7 can operate on more than 200 GSM providers worldwide, including AT&T in the U.S. It's also worth mentioning that compared with Apple, which typically charges $100 or so to add cellular data connectivity in its "premium" iPad models, Google is charging less to add it to the Nexus 7, particularly when you factor in the memory boost to 32GB.
Google Nexus 7 - Tablets - CNET Reviews