Pirate Ship offers great USPS discounts, up to 87% off, making it a solid pick...

https://high-wiki.win/index.php/If_I_Sell_on_Shopify_and_WooCommerce,_Is_Shippo_the_Better_Fit%3F

Pirate Ship offers great USPS discounts, up to 87% off, making it a solid pick for budget-friendly shipping. Support is only by email, which can slow things down if you need quick answers