The problem is pet stores. There are farms selling them cheap at 5-6 weeks, so pet stores can sell them cheaper than we can. Yes, there are ferret farms here, with the same purpose as mink farms. Therefore it's easy to assume some store bought ferrets were really destined to become furs, but if so it's number-wise only a marginal business for them. Normally, we feed them high quality cat food, for example Iams or Hill's.
Kitten food is just for puppies.
They get the yellow of an egg to share each week, and ground up cat vitamin pills every day. Apart from the meat, I think it's pretty typical. This is not common in Sweden, but may become so.