It is free to sign up with Shippo - we do not charge monthly fees, set up fees, or cancellation fees. When using Shippo you will pay the shipping rate plus Shippo's $0.05 per label fee for any live shipping label you create.
Shippo has discounted rates readily accessible through USPS and DHL Express upon sign up. Based on your shipping volume it is possible to lower these rates even more. You can find more out about that here.