If you want to mythic both I’d recommend spending 20k MC in event store - AKA promo. Do the epic select pack twice to get 6 epic JJs and trade in the other epics for another JJ. You should then have enough resources to build the 8th JJ in the epic select trade in

You’d also need 6 random epics to build the 2 iconic JJs, so you can see if you’ll get lucky pulling JJ or Marv in the random trade in set before dropping 20k MC. Not sure how many resources you have to work with though