Board Thread:Questions and Answers/@comment-25033368-20140607021333/@comment-10993019-20140626071721

I havn't either. Got one from a challenge.

Level 6 is where it starts getting really expensive (for example level 6 upgrade for F-16C, a very low-tier aircraft: 288,000 credits, more than the stock F-15C) so save those reports for the higher level planes because they're bound to be near 1 million credits an upgrade.