ebayPrice.js

function avergePrice() {
  var values = [
    ...new Set(
        $$(".POSITIVE")
        .map((i) => i.innerHTML.replace("£", ""))
        .map(i => parseInt(i))
        .filter(i => !Number.isNaN(i))
        .sort((a, b) => a - b)
    )
  ];

  const middleNumbers = values.length / 4;

  const firstHalf = values.slice(middleNumbers, values.length);

  const lastHalf = firstHalf.reverse().slice(middleNumbers, firstHalf.length).reverse();

  let sum = lastHalf.reduce((previous, current) => (current += previous));
  let avg = (sum / lastHalf.length).toFixed(2);
  console.log({min: lastHalf[0], avg, max: lastHalf[lastHalf.length -1]});
}

avergePrice()