I have the same thoughts as you. I asked the student in my interview panel if he turned to in-state, since he had mentioned that he was from Kansas, and he said no, that he can't unless he works full-time for a year or gets married to an Oklahoma resident. The other student in my interview panel got married to an OK resident and that's how she converted. The students who toured us around the campus were also paying out-of-state and cannot convert. You are right, it is a LOT of money. Before interviewing, I was under the impression that you can probably change to in-state after a year, but after hearing this info from the students there, it seems impossible. If I get accepted to a TX institution then I will rather go there.
I find it hard to believe that is the only way to get in state tuition. My brother went to grad school in TX and for in state tuition after a year and he never for married or worked.