It's a brilliant way to raise money. In all likelihood, the chance is probably not significantly greater than finding a shiny in the wild as a member, but simply knowing that there's that tiny chance that you can find a shiny, or that the ratio is something nice like 1/64 or something makes you want to give up the extra money.
Telling us what the chance is would probably deter a lot of people from spending those extra tokens, since the chance is probably far too low to warrant spending the extra $2.