Couldn't tell you price, but generally a lawyer will want to get to know the situation first, so it's not simply a matter of drafting the document, it's interviewing you and getting to know the facts and circumstances surrounding the matter. Some web based firms may offer to do this fixed cost if you want some price certainty. Whether you end up going to court will ultimately depend on the defamer's response to your offer.
The significance of a concerns notice is that in the event that the defamer responds with a reasonable offer and you don't accept it, that can be a full defence to any court proceedings that are instituted thereafter. Therefore it all turns on whether the defamer responds to your concerns notice, what their offer is, and whether you accept it.