Hi Joe,
I've got to hand it to you...your girlfriend sounds very special and quite the catch....very few women would eschew a real diamond for humanitarian purposes. Since your going with a faux diamond, I don't think it's necessary to hve a platinum band.......a white gold band will look just as nice and will save you a bundle which you can put towards the charity. For the synthetic stones, I like Ziamond as they have a lot of modern looking pieces....here is a link to a pretty 1.5 Assher cut ring http://www.ziamond.com/15ctroyascut.html in a white gold setting. Although some would disagree with me, no one will be able to tell a decent quality synthetic, CZ or moissanite from a real diamond. I would shop around and see which looks most stylish at the best price.
Another idea is to get a loose synthetic stone (in which case I might go with ASHA as their prices are cheaper for loose stones than Ziamond) and then have a local jeweler set and engrave it with a special saying on the inside...that would put an extra nice personal touch on the ring that she will be wearing forever.
