Why is he wanting the collection?

Is his main goal to have something to talk about and show off to others?

Is his goal to make an investment (I'm with KY Jon on this one, put your money somewhere else.)

Is his main goal to have something to do - looking for and learning about guns can be fun?

His reasons for wanting a collection will in part determine how he should go about aquiring it.

If he just wants a collection the simplest may be to just buy someone else's collection.