I use a carrier like this.
It's not heated, but you can use hand warmers as AHBD suggested, or use a small plug-in heating pad under or folded inbetween a fleece blanket.
When I would take my dragons to the vet in winter, I just folded a fleece blanket around my heating pad as mentioned above, but my car has an outlet. I also did not use these same carriers in winter. I'll probably wrap fleece around it in winter so the cold air can't penetrate it so much