DCS World 2.0 Alpha Nevada is now available for purchase and although expensive, it is a vast area with metric shit tonne of content. One issue at the moment however is the lack of campaigns for it, so unless you like making up your own stuff, perhaps its value is limited at this moment in time.
Here is the official blurb.
Digital Combat Simulator World (DCS World) is a free-to-play digital battlefield, focusing on military aircraft simulation. It includes a FREE TF-51D and an Su-25T attack aircraft.
DCS World 2 working with new Nevada Test and Training Range (NTTR) terrain module, that includes the largest contiguous air and ground space available for peacetime military operations in the free world. The NTTR land area includes simulated air defence systems, mock airbases, and several target ranges. The NTTR was also used for nuclear testing. Today, it is home to RED FLAG and other military exercises that include countries from around the world. The NTTR map for DCS World 2 includes Nellis AFB, Creech AFB, McCarran International Airport and the infamous Groom Lake AFB (aka Area 51). This map also includes the city of Las Vegas, McCarran International Airport, and Hoover Dam.
Additionally, DCS World 2 includes:
Powerful mission and campaign editors
Massive inventory of air, land and sea combat units and weapons
Fast mission generator
Dynamic weather and seasons
Mission replay system
Support for multiple maps
This exceptionally detailed and realistic world simulation engine guarantees an engaging, real-world combat experience in this flashpoint region. DCS is a true "sandbox" simulation that can and will cover multiple time periods covering many types of aircraft and ground vehicles. DCS World allows both realistic gameplay and more casual play styles to suit the player.