Yeah, pulling off "looking like a girl" will be a big challenge and unless you already have a passable figure there's really no cheap/easy way to do you. Most guys would need a corset and hip padding for that costume and something for breasts and something so you don't have crotch bulge - though you could modify the armor to just go over them. And you'd want a bodysuit to go over all that - and you have to affix the body suit to the breast "plate" if it's showing over the armor or you'll get that weird uniboob look.
If the hip/breast padding is enough you might be able to do without a corset - but you'll just have to try it and see.
I think it's good to talk cost because I find a lot of people are really overwhelmed by it their first time. I did some estimates for a friend of her material costs and we managed to get it down to about ~$250 - but that's still a shock to a lot of people who have never done a costume before.
With craft foam, it would be pretty cheap - but you'd still have to consider the cost of wig, fabric for a body-suit, any body paint/makeup, and whatever shaping things you need.
I'd kind of wonder about the armor bikini bottom. I'm not sure I'd want to trust craft foam to that - you'd probably want to reinforce it with something like vinyl - or just make it out of something like vinyl, paint to match, and make details in craft foam.
Doable by November if you have the time, yes. I know that I personally work ridiculously slow so I know I'm pushing it asking myself to make two costumes by September. I'd guess someone who isn't such a sloth would have an easier time with that aspect. :P
Disclaimer : This post written by a Grumpy Old Man
Actually in the pipes:
- Remaking Ser Loras doublet.
- Luke Skywalker, A New Hope
- Wind Waker starter costume in swim material
Eventually: Paul from Dune, Faramir, Harry Sullivan