A Question for Y'All

I've got a question for anyone and everyone who happens to be in the National Treasure fandom (which I will be crossposting on my tumblr). Where in the hell is Ian's motivation for finding the treasure explicitly stated to be monetary gain? I see this notion in nearly every review of the movie online, but there is literally no evidence for it in the film itself, unless I've missed it. For all I know, he's probably bored out of his skull and needs something to do with his life and this just happened to fall into his lap. Seriously, where does this monetary gain thing even come from?