Ansett is a good guide for this, the liquidators in their report valued points at US$0.0015 (Ansett points are worth less than AA or UA miles by about 1/2), based on the COST of the points to Ansett. Note that this also includes the marginal cost of flying the pax on their own metal. I would guess that each mile is worth about .5 of one cent in interchange fees to the airlines (but note that they would also get a credit for paid flight miles that their members make on each other, which in most cases will contra the reward seats used), which would be in line with the costs they pay each other for "staff fares".