Several thousand dollars. It's more than just swapping out the transmission... you would have to reconfigure the pedal setup, the center console, and you would have to swap out the main engine wiring harness and computer. Plus you would devalue the car since the VIN number and title of the car would show that it is an auto and now it is a standard.
If you want a stick, it would be cheaper for you to sell your current car and buy one with a stick