Price has gone down. I rarely see such rates unless it's a high-profile magazine like The Peak.
For smaller periodicals actual figures are more like $100-$200 for internals. Doesn't sound like much of a price drop but it's actually 30% less!
Considering it's an inflight magazine I would assume $100-200 also unless it's SIA, Lufthansa, British Airways, basically the 5 star airlines. But AFAIK, SIA doesn't randomly source photos, and I would assume that it would hold true for the other airlines too.