Re: joining a box
My wife and I have a CF "home gym" set up in the garage where we can tackle just about any workout that may come. However, we rarely use it unless we are following a specific program (usually a strength program) that the gym may not be following. I think we both find that we get much more out of going to the actual gym. I know that I personally work much harder when I'm with other athletes vs by myself. I make lifts and PRs much more often when in the company of lifting buddies vs in a hot, lonely garage.
I think there are many benefits (coaches, partners, atmosphere) to actually going to the gym that make the cost worthwhile. Use the garage for your specific goals if they cannot be accomplished on the gym's schedule. Fortunately, we have a really good gym with a lot of open gym time and like-minded individuals that are into the same programming and goals as we are.