Congratulations! 
Here is a link to many articles on the Offbeat Bride blog featuring brides in pants and other non-traditional garb. They have a companion forum-type network you might find interesting, too.
Can at least one of you get away with wearing a tux? Or a military uniform.
CrazyCatLady already mentioned them, but I just wanted to second that JCPenneys generally has very reasonable woman’s evening-wear. By “very reasonable” I mean stuff that doesn’t look like you’re going to prom or a nightclub. I didn’t see much online right now in white (except for this B/W jacket or ivory top?) but stock rotates and sometimes the stores have stuff that’s not in the catalog.
Anyhow, I wanna play along so here’s a few ideas, note they are just patterns so more for inspiration:
lace jacket
like the alfred angelo one
another tunic
ETA: Congrats!
I would think very seriously about seeing a professional seamstress.
Yeah, I vote for the skirt also.
…or maybe a kilt.
Go to a seamstress.
Two similar, but not identical outfits that both fit and suit the wearers perfectly is a big ask.
You may find two off-the-peg outfits you each like, but the colours and trims might not quite work together, meaning one of you would have to compromise (and a girl should never have to compromise on her wedding dress).
A seamstress on the other hand…she could make two different outfits in the same fabric with the same trim, or two identical outfits in different fabrics with the same trim or any variation of that.
If one of you wants a Shalwar kameez with a nehru collar and the other wants a bolero, camisole and palazzo pants having them made by the same person is going to be the best way of getting them to work together.
If you have different skin tones, finding the right ivory/cream/white shade that suits you both may also be an issue (no, really, it might). Having a seamstress make outfits from scratch means that she has every shade available to her- many bridal shops will offer you white/ivory/cream and you have to hope you suit one of them.
You’ll also have the advantage of having your outfits cut and fit to suit your figure exactly- rather than cut to suit hundreds of people and then fit to you.
I’m biased of course- my wedding dress was made by a wonderful seamstress and I found the whole experience fantastic.
Oh, Queen Tonya beat me to Offbeat Bride - I absolutely second this recommendation. Lots of general ideas here, plus the entries will link to specific vendors if the idea is interesting.
And congratulations!