How much does a body computer cost and does it fix starting problems?

What is your question?

My car periodically will not start and goes into failure mode. the exterior lights and interior lights flash in a sort of "Morse Code" pattern until the battery dies down. I have replaced battery twice in a year and replaced the key. No brake lights are out and it is not a constant problem. I can't drive the car because I don't know if it is going to leave me stranded. It was recommended to replace the computer. The two suspects are the body computer and the security computer. Does anyone know what the expense of this is and if it might be effective.