They opened one seat back up in I class on 10/30 return (hopefully you only need one ticket). There are seasonal discounted fares around Labor Day, Halloween, T'giving etc. for I and Z fares which is why going from a D fare to an I fare reduced fare so much (the seasonal fares are valid for Oct 29th - 31th returns from the EU). There is Z bucket open on flights on the 31st which would save about $550 and reduce total roundtrip to $4300. There are also cheaper Z fares for Tue-Thu departures from US (Fri-Mon departure Z fares are $350 more). So flying out Tuesday instead of a Sunday would save another $350. So total roundtrip price of $3950 is possible with Oct 22 - Oct 31 roundtrip and $900 total in savings. Many people want to be home before Halloween day which is likely why there is cheaper Z bucket inventory open for 10/31 returns, but not 10/30 returns.