Hi Thomas,

Thanks for contacting us here.

Could you please provide more details about what you are trying to achieve? I'm not very clear about which can be useful for your case.

If this surcharge is simply an amount added to the subtotal of the bundle, it's impossible. Some users use the Extra Product Addons but it causes some pricing issues.

If this surcharge would come in form of an extra product, you can either use the WPC Frequently Bought Together or WPC Force Sells to add extra products to a smart bundle, composite product, or grouped product.

WPC Frequently Bought Together only adds optional products, while another plugin from us can add required products called WPC Force Sells. 

If you want to offer your customers a product A, and they can choose either B or C or both as extra items, you can use the WPC Frequently Bought Together.

If you want to offer your customers a product A, and they must buy both B & C as extra required items, you can use the WPC Force Sells.

You can use both of them in a product since they're can be added from the product tabs: https://www.screencast.com/t/zsdI0WuYBht5.

In the front-end, you can have a deal like this: https://www.screencast.com/t/5yJXzy4Orsow.

We have written a blog about how to create deals with our plugins, you can kind refer to it: https://wpclever.net/5-best-woocommerce-product-bundling-tools-for-skyrocketing-your-sales.html.

Or you can simply create a composite product with our WPC Composite Products plugin, use the Include base price pricing method for it. The price you enter in the General tab of the composite product page will be the base price. The subtotal will be the sum of the base price and all components.

You can read this documentation for more information: https://doc.wpclever.net/docs/wooco/.

Best regards.