Cat food has too much protein in it for rodents but dog food is fine as long as you feed a high quality dog food. I wouldn't recommend this be their only source of food though. After all, dog food was formulated (poorly) for dogs not mice.
The dog food we buy for our dogs is like 50 bucks a bag so its pretty high qulity.
How big of a bag is that? You can probably by Mazuri rodent feed a lot cheaper. Check you local feed store. I get a 25 pound bag for about 15 to 20 bucks.