Rakuten is offering the white or copper 3rd generation Nest for $196.99
today (10/10/17) only with coupon code GGNEST
at checkout ($228.99 before coupon). There have certainly been been similar/better deals over time, however, at the moment this is the best one I've been able to find. Note: check with your power company...if you can get a rebate from them, it would certainly eclipse any deal you'll find. Shipping is free, tax in CA only.
Nest 3rd Generation White [rakuten.com]
Nest 3rd Generation Copper [rakuten.com]