After 2 days, I had spent 1050 crystals (spent 3 x50 refreshes just before the event went live, which was technically the previous day from the game's point of view, then 3x50+3x100 for each live day of the event).
At that point,I was at 43/80, which was just slightly above the listed drop rate of 20% for my 10 energy node (I'm farming gear exclusively)
285 + 360 = 645 = 64.5 attempts/day with 3 days remaining. The final 1/2 attempt won't count for anything, thus...
At a drop rate of 20%, that's 0.2 * 193 = 38.4 new blueprints expected from 450 more crystals.
43 + 38 = 81 blueprints on a total of 1050 + 450 = 1500 crystals.
So, if you pre-spent to load up on fleet energy, you could just barely get to unlock on 1500 crystals. I'm really not sure where anyone got any ideas that it would be cheaper than that.