The 300 for the sensor install alone is too much but I would guess diagnostics is included in the charge so that makes it a little high. You can do the job yourself but I would buy the sensor from the dealer and it will look different. The new upgraded version will be black and support itself on top of the two hoses. If you don't have a scanner to clear the code just disconnect your battery for a few minutes.
2015 XLT Supercab 4X4