i've just bought a linen colour block dress in m & s for £35, and a black jasper conran fascinator (like a big dinner plate on a hair band, with bits sticking up) in debenhams, reduced from £40 to £28, all for a wedding next august. i already have a black bag and sandals, so that's me all set up.
i really don't believe in spending a fortune on wedding outfits and i'm sure you'll look lovely in your frank usher jacket (i have a wide, stretchy,black sequinned belt of his, it was all i could afford at the time, absolutely love it) with whatever you decide to wear with it :o)