My father-in-law lives in Scottsbluff, NE and we go prairie dog hunting there often. There are prairie dogs as far as the eye can see.
He is a seed/fertilizer dealer and knows a lot of the farmers around the area.
It might be a little farther than you want to go, but not much. You really have to get into the Nebraska panhandle before there are a lot to shoot, although there are some around the Kearney, NE area, but none for shooting.
Within your 10 hour range, I am thinking that there might be some closer in South Dakota, but I am not sure.
I do know that there are a lot of people in Scottsbluff that want them gone.
When are you wanting to go?