.Gov is a domain name extension that is only available to registered websites of governmental entities in the United States, including federal, state, local, and tribal governments.

At the recommendation of the General Services Administration, the cost of a .Gov domain registration and renewal will increase from $125 a year to $400 a year effective January 1, 2017. 

There are some jurisdictions whose renewal period (90-day window) may hit before the end of this year. If this applies to your jurisdiction, you should take advantage of that renewal as GSA will honor the existing $125/year price.