Yeah, eBay's fee system can be pretty overwhelming at first. What you need is a proper eBay fee calculator specifically for the UK market. These tools factor in the final value fees, payment processing costs, and any promotional listing fees. I've used one that's pretty accurate - you can find it here
https://easync.io/ebay-fees-calculator/uk/ . Just input your item price and category and it breaks down all the deductions.