I have coolant warning messages (low level and stop now) that used to be intermittent and is now permanent.

The coolant itself is fine, the local shop verified this. I also have driven this for 6 months with no driving problems.

The shop seems to think it is the sensor in the water bottle.

Is this a big deal to fix (time and money). Can it be a do it yourself job.

 

It will take you about 5 minutes to replace it.
Not sure about price though.