How's the costume progress coming? I have some things that might help:
You can try using millinery buckram instead of wonderflex for the neck piece, since it's cheaper than Wonderflex. I've made hats with it that had a very similar shape.
The Pepsi logos aren't that difficult to do, depending on what material you make the gloves and boots out of. The easiest way to apply the graphics would be to make the boots and gloves out of vinyl and have some custom vinyl printed decals applied to them. You can even design, upload, and buy vinyl decals online and have them shipped to you.
The corset looks more like a one piece bathing suit with piping and metal boning than an actual corset. Have you considered getting a swimsuit and modifying it? The aqua clear parts can be done with clear vinyl and wire supports.
And those are the easy parts! How are you making the thorny tentacles, gun, and fingernails?