"settling" for the ATX (no offense to ATX owners, I am a former) will put a large damper on your 14's. Not saying you can't DO it.. just realize that it will take more in an ATX to acheive the same goal as in an MTX..
If you truly want an MTX, broaden your search area a little...
What part of OK are you in? Have you been in the South Central forums on CEG, yet? Check the classifieds on this site, as well.. I have seen MTX duratecs for sale like crazy, lately. Its nothing that a quick flight and a well deserved "aquaintence drive" won't fix, if it is out of state.
Ray