Our local directory assistance is two calls for free, then around 35c a call. I believe most places charge something like that for local directory assistance, and $1 for long distance directory assistance.
At one time directory assistance was a profit contributor in that a customer wouldn't be making a call without the number. In a day when most calls were metered that was important. About 50 years ago and longer, many people made long distance calls by name and city, not by number "operator, get me John Smith in Kansas City", and the operator would call KC information to get his number then make the call. The Bell System ran ads to discourage that and to call by number, then provided free distant information.
Over time however, the company found costs growing and many people using DA because they were too lazy to look in the phone book or to verify someone's name and address. So they began charging for DA use.
What bothers me is that many sources are INACCURATE. My own listing is totally fouled up on some alternative sources, though it is correct in my local telephone directory. The same alternative sources have an old number long disconnected still shown as in use. If someone tries to use one of those alternative sources they won't be able to reach me.
But I must admit in a way I'm glad those alternative sources are messed up. If someone truly wants me, they'll spend the 25c or $1 and call standard directory assistance and get my listing. I suspect the alternative sources are more of a resource for junk phone solicitations and junk mail. Charities and politicians are still quite heavy users of telemarketing. Some sleazy businesses call up and say "you've done business with us in the past so we're calling you today ..."