If you want to purchase games "a la carte" - it's easy to make purchases without becoming a subscriber of either Club iWin or All Access.
After you exit a game or select to buy a game, you will be directed to the following screen below:
Here you may select 1 of 3 options; the first two being subscription related (All Access and Club iWin) and the third option being an out-right game purchase.
In order to purchase a game without a subscription, you would select the "Buy it for $9.99" option.
After you have selected 1 of the 3 options, you will provide payment info and taken to the shopping cart to confirm your order before submitting.