In order to use Express Checkout you must have API credentials from PayPal for this. If PayPal is telling you that you need a business account for this then you will need to sign up for one to gain access to the API. This is PayPals checkout system that is supported in PowerStore, we can only go by the requirements that they have for implementation and use. From what digging I have done the info seems to be saying that you can sign up for this Express Checkout service without accuring fees. This is something that you should discuss with PayPal for more clarification.