If you check some of the armor threads on this forum, you can find some tutorials on using craft foam; that's probably the cheapest, easiest thing you'll be able to make armor with.
Her chestpiece looks more like leather to me... If you want some easy texturing on that, you could make the base out of foam and then cover that in an upholstery vinyl.
Def up for interpretation though; it looks different in every art I've seen her in. x_x
As for the chain maille, instead of going the authentic route, you can chop up some pvc pipe and still learn how to make it.
Or there are other cheap alternatives:
You may be able to Google fabric that already looks like maille as well.
Good luck! Always nice to see more Magic costumers.