From what I've seen the rate for 5* unspecific is 0.6%, it's a bit below the industry standard. There is the 90 roll pity though. assuming you don't get any 5* by 90 rolls.
0.6% is quite close to 0% so I'll assume that no 5*s before 90 rolls as that is quite possible. As without pity at 90 rolls your chance at a 5* is only 54%.
We'll also never do single rolls and 10 rolls only. the cost of 10 rolls is 1600. 1600*9 = 14400 which is the final cost in wishes for unspecific 5* in premium currency.
Based on the what the largest pack is worth in other similar games we can expect the largest gem pack to cost somewhere between 90 and 100 dollars. In CN the largest pack gets you 6480+1600 gems = 8080 gems total. That's probably fairly accurate. If we infer 8080 gems = 90 dollars and the cost of 5* unspecific to be 14400 gems then we can see the cost of a unspecific 5* to be slightly less than 180 dollars since usually buying the largest packs give the most bonuses people tend to buy those.
TLDR: 14400 gems for a 5*, runs about 180 USD
