(second time around, I wrote a long post yesterday night, but then the forum froze on my tablet and I lost everything!)
Even though I find your skirt+top+blazer (I LOVED the double polka dots: on the top and on the wonderful hosiery!) beautiful, I wonder whether you will feel comfortable being among the few not wearing gowns for this event. As you described your friend's shopping strategy and the preparation for this event, I got the impression it is rather on the fancier side of things...
If I were you I know I wouldn't fell comfortable if I wasn't wearing a dress (call me vain; it hurts, but it isn't untrue...). Keeping that in mind, I selected a few links for you:
1. H&M
A. A 40 euros dress that has a very similar material composition of your ESPRIT dress (more than 90% polyester), but cost obviously half the price. It is from the new Pre-Fall collection, so I guess you won't have problems finding it in the B&M shops.
http://www.hm.com/at/product/14014?article=14014-A
B. If you are confident about separates, I would still go longer. I'm emulating one of Angie's Pinterest (http://pinterest.com/pin/18577417183994324/) outfits tonight with this skirt. I vouch for the navy version of it: I assure you it pass the "eye-test" for quality material (it looks better than it actually is; it's a 100% polyester garment in the end!). For your event I would suggest pairing it with a black turtleneck sans any toppers.
http://www.hm.com/at/product/1.....le=13581-A
The dressy heels you have will go with both options.
Mango is on sale round here ATM. Do you have it in Berlin? They also have a long, cobalt blue gown for less:
http://shop.mango.com/AT/p0/ma.....;s=prendas.