Caspian is different, I don't think it's girly. IMO the person makes the name, not vice versa. I wasn't a big fan of either of my boys names, but now I can't imagine them as any other name.
As to Cash and Cash Money, good luck with that. I have a good friend who wanted a Jimmy. He didn't care for the name James but went with it figuring Jimmy would catch on. It didn't. A neighbor's son was the third Karl but he wanted to call him Trip. That didn't make it past elementary school. If you want to call your son Cash, name him Cash. If you want to call him Cash Money, reconsider.
Whatever you decide to name him, all the best to you and your wife!