I vote for A, with the recommendation that the third pack is from the M13 core set, since it uses basic mechanics that will mesh fairly well with MM. The block expansions don't draft well with sets from outside their respective blocks (especially not RTR block). I really want to draft with this set (at least a little bit) so this is the best option, I believe. I can get friends to purchase their own draft packages to put together a full draft.
For that, I'm guessing the price would be about $17 - 20, right? Approximately $7-8 for each MM pack, and $3-4 for the third seems fair, given the MSRP. I think I'd probably be willing to pay up to $25 for it, but I don't think I could go over that at all. $50 for two people to play in a draft is quite high, considering this is only 2 packs of the desired set, plus an almost-rotated filler pack.
I'm confused about what you mean with option B; is that a package of three different boxes? That seems very strange to me.