9to5Mac managed to find a reference to the $4.99 price in an API used by the App Store app. It also mentions a month free trial before the payment kicks in. It also confirms that Apple Arcade will work with Apple Family Sharing, so you will only need one subscription to give access to everyone in a group.

With Apple’s regular iPhone event mooted for 10 September, it’s likely that we’ll see the price announced there - though of course it might change, and be different according to country.