Was the rarity of the infected hau the same as every other mask? So far, at least for the US version, the odds seem to be that each mask has a 1 in 73 (1.3%) chance of being in the box. That is assuming that an equal amount were made of each mask for the packs.
If that is not the case, the odds will change.
I do not think that the prices on bricklink are always accurate to initial rarity. For instance the black kanohi tend to be more expensive, but I chalk that down to people building 2001 shadow toa.
Also, I'm really glad you guys are willing to help!