I've had the mobile tech come out here oh about 4 times in the last year or so. Yep, based out of Winnipeg, technically though works for Toronto service center with a Toronto phone number. The Edmonton mobile tech *may* go to Saskatoon but Regina & southern SK should be covered by the Winnipeg tech.
If he is coming out to work on multiple cars on a scheduled trip, there is no fee. If he has to come out specially for you (e.g. urgent issue), the fee is $1,500 (it's based on distance but it's basically $1,500 for everyone in Saskatchewan). That fee is for coming out, it has nothing to do with whether it's warranty related or not. Winnipeg folks never get charged that.
It seems the tech comes to SK about every 4-6 weeks. I'm on the list for when he comes next. And yeah he worked on my car last time he was here (early April). Keep in mind the mobile tech can't do everything a service center can (I made the trek to the Calgary service center in January to address those issues).
And for the record, everything I just wrote is subject to change. The mobile (ranger) policy has changed many times in the 4 years I've owned Tesla.