Step 1: eBay listing fee:
Free if you're not selling more than 20 items in a month (or only 35p otherwise)
Step 2: Optional extras:
£2.50 for a larger picture (except for Clothes, Shoes & Accessories, Cars, Motorcycles & Vehicles, Home, Furniture & DIY or Pet Supplies, where it's free)
50p if you want to offer 'Buy it Now'
Step 3: Final eBay fee:
10% of the sale price (including postage).
So, if your item costs £20 for p&p, that £24 to pay.
Step 4: PayPal fee:
20p + 3.4% of the amount paid (which obviously includes p&p).
So, again assuming £20 for p&p, that's 20p + £8.16 = £8.36
[NB: Higher charges are payable for sales to buyers paying in other currencies].
So, roughly £32 as a total.
http://sellercentre.ebay.co.uk/introduction-ebay-fees
https://www.paypal.com/uk/webapps/mpp/paypal-fees