I suppose I wouldn't feel comfortable paying more than 50% of monthly income for a flight. Once it starts getting to that level I'd be thinking about how I could spend the difference between Y and J on the actual holiday!

A few times a year I come to NYC for a long weekend and am happy to pay for J, particularly on the way back to Europe, in order to get a decent sleep without having to take an extra day off work.

In a couple of years when I have to pay for 4 tickets for the family it may be a different matter. Hopefully the children won't have got too used to F/J by then!