The only way I could think of making this for as little money as possible was using polymer clay. So I went to JoAnn Fabric's and picked up all of my supplies (Thanks for the giftcard NT!).
Things You'll Need:
polymer clay, ribbon, jewelry wire, scissors, jewelry wire pliers/cutters, glue, an oven
I don't have all the steps for this DIY (picture-wise) because I ran into some difficulties, but here it goes.
Step 1: Shape the polymer clay into pieces similar to the MARNI necklace.
Step 5: You should have two pieces of ribbon and loop them through the top of each magenta piece. Then glue the ribbon to secure it and use a small binder clip to make sure it keeps it contact while it dries.
And then you should have a fabulous MARNI-like necklace of your own. Is it exactly the same? Nope.. not really, but I spent less than $10 on this!