AFL has released their ticket allocation
https://s.afl.com.au/staticfile/AFL Tenant/AFL/Files/2018-AFL-GRAND-FINAL-TICKET-SCHEME-FINAL.pdf
16,000 - 40,000 tickets set aside for competing clubs.Presuming a 50:50 split between us (if we make it) and either Richmond or Collingwood, that is 8,000 to 20,000 each
It's been publicised elsewhere on Demonland that we have approx 10,000 Priority 1 Members. This leaves anywhere from 0 - 10,000 P2 and P3 tickets available.
45,000 members approx total - 10,000 P1 ticket holders = up to a 28% chance