I'm actually surprised to hear so many who don't offer hot dogs. I thought all theaters did as a staple item. Live and learn.
One of four theaters in an area I used to live in offered $1.00 hot dogs, and I always chose that theater over the others just for that reason, all else being the same. I still payed $4 for popcorn and $3 for a drink, but I would have at the other theaters anyway. They may not have made much, if any money on the hot dog, but they still got my repeat business because of it.
If you use a rolling hot dog warmer, like the Gold Medal machine, you can also use it for other rolling items, like Churritos. Here is an excellent article on Hot Dogs for retail sales:
http://www.provisioneronline.com/FILES/hot_dogs.pdf