It's not that hard to keep them inside. From experience they will thrive with the right set-up and proper food. I think the regal horned lizard is one of the most prolific species. I'm not sure about the Texas horned lizards, though. Which one are you getting? Those are two species are the most commonly kept species I think and their should be care sheet on Phrynosoma.org. Check out the site for care sheet!
www.phrynosoma.org