Unless your brother in law is a serious collector a contemporary rifle might be more pleasing and you can get one that won't need to be coddled for fear of scratching or breaking it. While plain, late, original rifles can cost less than moderately priced contemporaries, the really interesting early rifles in reasonable condition are typically 10X as expensive.
Of course not all contemporaries are the same. There are master's making them and what my Dad used to refer to as ham and eggers. Very few contemporaries are sold through dealers, most of the better makers build to order for customers. That said, there are a few people who handle sales of used contemporary rifles on a consignment basis. Jim Chambers
http://www.flintlocks.com/ usually has some good contemporary work available on consignment. He's a fine, honest fellow. If you could identify a style of rifle that appeals to you we could also recommend various makers whose work is in different price ranges. Feel free to message me and we can discuss this more off the board.
Tom
