I am actually quite shocked that Eugenie is so high on the list. She is fairly low in rank and I have my doubts as to her husbands bank account - I would certainly assume it is lower than that of her brother in low. And while Beatrice is also obscenely high up, she is just a tad more than half her sisters.
I would imagine she gets a lot of free/discounted clothing that UFONM is counting at full price. She’s often in the papers if she wears something new, so giving her clothes is good business for the designers.