I just ordered one of these to experiment with for my heavy lift hex, and am looking at the Mavic too....
For a full GPS tracking device, (as long as cell reception), doesn't  look to bad. I just have to modify the battery supply wires to get rid  of the collar itself. 50 bucks for the hardware, and 8 bucks /month for  cell services.

https://pawtrack.com/

Let you know in a week or so.....

Hi, thank you for reaching out and sharing these  information. Just a friendly reminder that DJI does not recommend you using a third party device or accessory when operating of flying your drone. The said third party device can affect the said drone when flying and may lead to a crash. Please fly with caution with the third party device attached on the drone. In addition any crashed caused by third accessories or application can void the said warranty of the drone. Please refer to the images I have posted. Thank you and fly safe.