Mazda Repair: Miata 1991, houston area, manual transmission

Question
Can I replace the manual transmission in this car with an automatic one? How expensive and who do you recommend in the Houston area?

Answer
It's possible to put a manual in a automatic Miata but not vice versa.  The automatic  transmission is electronically controlled and your manual is not equipped with the harnesses, the controls nor the cooling system required to make it an automatic.  Sorry.