how expensive is it going to be and how dangerous is it to be driving my car like this.?

Question

My engine light went on and it's P2138

Answer 1

P2138 Accelerator pedal position (APP) sensor 1-2 correlation

Very dangerous, what happens you can be going down the highway where there is no safe turn off, and vehicle goes into reduce mode, As for the cause this depends on, this sensor is located on the accelerator pedal, from a faulty connection to a faulty accelerator pedal.