First, let's start with the belt (that's the easy part): You can find BCBG's multi-colored belt for $68 at Lord & Taylor. It's unique and might be worth the price if you think you'll wear it often this fall and beyond. You might also try making a DIY version of this belt using some colored thread!
Now, on to the dress. When you're looking for runway-inspired pieces, your best bets are Zara, ASOS and H&M. Here's a mixed print dress that captures the feel of the Dries pretty well ($196, ASOS.com):