RE: Oorah raffle ribbis issue:
The Shulchan Aruch (Y.D. 176:15) allows a dowry to be structured in a way which has an increased amount if the payment are delayed. The posek I spoke to (he answers Choshen Mishpat and ribbis shailos daily) was mattir the Oorah rafle on these grounds. It is similar to the dowry, which has the status, for ribbis, of a matana, as does the raffle.
It seems that Mod 42 and Joseph are correct that it is considered (despite the wording) to be a choice of two different prizes because there is no chov (obligation) based on a loan (or sale, which would have been ribbis d’rabbonon).