The Devil's in the Details
What Does Google Maps Cost Me?
Google maps was free for many, many years. But once it become a needed commodity, Google saw a way to monetize it, and is now charging for its use. So how much will it cost you to have on your site? Well that depends. Google gives you the first $200 worth of uses each month for free. For many businesses that only have it on their Contact Us page, that's more than enough to handle the cost. You still need to sign up and register a credit card, even for the "free" use.
See Google's Map Price Sheet
Instead of printing everything from the article above, the summary is that the cost is roughly $2 to $14 per 1,000 requests. Pricing is different for each type of request that's asked (map, street view, etc.), so you'll want to review the pricing above in depth so you can calculate and get an idea of what your monthly costs will be.