Hello,
Here is some information on the pricing scheme for Shopify Marketplace Connect, found here:
https://www.shopify.com/pricing
The app is free to use until you reach 50 managed orders (from connected marketplaces) every month. On the 51st order onwards, overages will be incurred amounting to 1% of the sales, up to a maximum of $99.
Any fees associated with selling on eBay and Shopify are charged separately.
If you have any other questions or concerns, feel free to send us an email at marketplace-connect@shopify.com or click on the Chat button on the lower-right portion of the Marketplace Connect app.