no, power store does not offer a way to make the shipping dependent on the total price of the cart.
when using FedEx shipping, make sure you entering the correct Account and Meter number information, when the shipping lookup fails, it is usually due to incorrect account and meter number.
also make sure your products have a weight value set, the fed ex rate lookup is based on weight, if no weight is set for the products, it will case rate lookup to fail.