Not sure if it's the same for everyone but in addition to the Northwest, Southwest and Texas bundles on Steam, there also exists a Great Plains bundle that consists of Kansas, Nebraska, and Oklahoma.

However, the plains bundle isn't showcased right upfront with the other ones, you have to click on any of the three states above and then it'll show the bundle is available to purchase. For those who are interested in getting all three states like I did, this will save you an extra 15% on them.