I was looking at different telephoto lens bags on amazon that would fit the Mavic and this is what I decided on getting, it looks like they just sold out but you can pick it up for a similar price at other stores if you search google. Based on their listed internal dimensions it should be able to snuggly fit the Mavic and either a spare battery or the controller. Way cheaper than the DJI bag and smaller form factor too!
https://www.amazon.com/gp/product/B009KY5YOY/ref=ox_sc_act_title_1?ie=UTF8&psc=1&smid=ATVPDKIKX0DER
https://www.amazon.com/gp/product/B009KY5YOY/ref=ox_sc_act_title_1?ie=UTF8&psc=1&smid=ATVPDKIKX0DER