US Cellular is now selling the Nexus 6, starting at $200 with a 2-year contract, the 64GB version is a $50 upgrade. You can also grab the device with a pre-paid SIM at $660, but 64GB storage will cost you an extra $70.
AT&T has already started shipping the device at $250 (32GB) or $683 off contract. Sprint is asking $300 for the Google phablet with a 2-year contract. There's also T-Mobile which is asking $650 for the 32GB model and $700 for the 64GB (no subsidies here though).
Verizon is yet to officially offer the device, but the Google Nexus 6 does work on its network. For now though, US Cellular seems to be offering the best deal for the Motorola-made phablet.