Cobalt Rivets ~43. Cobalt Mesail to 50.

That seems like the most obvious path. You can even squeeze out some extra exp by dying the mesails.

I haven't done Armorer yet but I intend to.

I know you don't want to hear leves, but they are the most ideal method through the 40s.

You have to spend something at this point. Gil (to buy mats), time (to farm mats), or Leve allowances.

Through the low 40s they'll reward 2800-3500 upon turn in. The 45+ leves should reward about 4000. The 40s are where where leves really shine for crafters.