How do I add a separate one of charge when customising a product, no matter the quantity?

[colettetoman]

Hey 

So this is an embroidery business, but to set up a new logo there is a one off £25 charge that needs to be separate rather than built into the item cost. So it can't be added as a variant, because if someone orders 10, the £25 fee would be built in and charged 10 times. 

 https://apembroidery.co.uk/products/branded-unisex-t-shirt 

I have set up customisation choices using the variant option app but it doesn't allow to charge a cost as far as I can see. https://apps.shopify.com/variant-option-product-options 

I need to set it up exactly how it's set up on this website: 

https://thegraybearcompany.com/products/result-polartherm-fleece-jacket 

Thanks