The answer is yes. You do not need to be subscribed to be able to purchase icons or icon sets on Iconfinder. Instead, you can use the Pay-as-you-go option (to buy icons on demand without being tied to a subscription). To start buying icons, you first need to make a prepayment to your Iconfinder account balance. For this, follow the steps in this article: How to make a prepayment to your account. Once your account balance is positive, you can already start buying icons.
Please note that in order to add money to your account, you must be a registered Iconfinder user.
Read more about the Pay-as-you-go option.