For anyone worrying about the rng part of the event and the min-avg-max number of crystals, I will copy my post from /jp/ over here.

I shall hereby present you: The ultimate calculation to lay everyone's rng fears at rest! (assuming they can clear the last map)

First: Look at the min/avg/max table for your stamina. The avg number of crystals should allow you to, after clearing the previous maps, run the last map around 92 times, if you start with full stamina and make full use of what you regenerate. I'll assume the worst case scenario of you having only 12 stamina, i.e. each additional crystal gives you 2 more attempts at the map, and for ease of calculation I will assume that you got absolutely 0 serums from any of the previous maps.

(For those interested in the method to check what I did: C=Number of times you cleared the last map. I calculated the chance of getting at least (1200-C*10)/3 hits out of C*2 rolls)

Here are the results:

Chance of not maxing with +1 crystal: 10%

Chance of not maxing with +2 crystals: Roughly the chance of drawing Nanaly from Premium Summon

Chance of not maxing with +3 crystals: Roughly the chance of getting a 4 of a kind on your opening hand in Poker (regular 5 card draw mode)

Chance of not maxing with +4 crystals: Winning the lottery

So basically, if you have even just a few more crystals than the average from the table, you are fine. On the downside, this also means that you can't hope for luck to save a few crystals either, since the chances behave similarly in the opposite direction.

tl;dr: Expect to pay pretty much the average from the posted table above with almost no deviation. I doubt there will be any player paying more than 3 additional crystals, let alone 4.
On a side note, this is all assuming you never mess anything up, so it's probably still a good idea to have a bit of a safety net, in case you fail a map. If you're worried you can't clear the final mission, but can clear the 2nd to last map, I would roughly estimate that you need something like 2-4 ish more crystals. If you can't clear that one either, you should probably give up on maxing her unless you're willing to spend around 50 crystals for it, but getting the black one is still within reach with a reasonable number of crystals.

Also, as a little bonus calculation: If all the little particles in the entire (observable) universe had an Aigis account for the event, you would expect around 100 of them to pay the "max" amount.