so if i fix error I (o2 sensor) that may fix the Fuel prallem?

also lately in 3rd gear around 2-4k rpm i get huge power loss sometimes that feels like the car wants to die.

im only puting 93 octane and used an injector cleaner in the first and second full tank.

How much is an o2 sensor for this car? where can i get a good price? and where is it on the car?