1x Ex-Wild = 3x R-Gacha and 3x R-Gacha have around 4-5% chance of giving SR-Girl.
I got my first 3 SR-Girls with 3x R-Gacha
Expect to spend 50-100x R-Gacha per SR-Giirl if you donate 1x R-Gacha or 3x R-Gacha.

I been testing 1x R-Gacha for a week and got this data so far
72 R-Gacha spend (used 74 but get 2 back)
590x Candy
49x SR-Wild3
6x SR-Wild1
12x R-Wild
10x Paromanin half
8x Pudding half
2x R-Girls
2x N-Girls
1x Pudding (wating time 1:30 only)
2x Glasses (waiting time 2:00 only)
2x R-Gacha (Wating time 1:30 only)

Wating times:
69 x 0:50
1x 1:00
3x 1:30
1x 2:00

I will post again when I got more data.