£50 seemed a good deal including shipping from Australia, it didn't even have a warning that I may incur taxes and duties.
I feel for you, Alexis. I've long since stopped buying from abroad unless I really need to. Particularly with the pound being practically worthless since Brexit.
It used to be buying stuff over £18 incurred charges, and even then it seemed that it was mostly stuff from the US that was checked and so was less risky to order from Australia, Canada, Japan or wherever on more expensive items.
Now I believe the item you can be charged if the value is lower than that. Particularly if you have an idiot seller who includes
postage costs in the total they declare on the outside.

(though to balance it out, I've had some nice surprises when an item I was expecting to come with a customs charge got delivered without).
All the same - and I hope this will make you feel better about it - £13 extra is pretty good for an item of that value. Royal Mail charge something like an £8 handling fee regardless of the cost of the item, and then the import charges on top of that start at about £3. So you're not too far above the same as you'd be charged for an item with a value of £16.