Is there a car service in dengfeng, henan that travels to shiyan in hubei, China? How much?

There is no direct bus between the two places.
You can go to Dengfeng General Bus Terminal to take buses for Zhengzhou Central Bus Station. From this station, there is only one bus at 18:40 to reach Shiyan and cost around 7 hours. I just know there is such a bus, but I am not very clear about the ticket price.