Tights are very much back in style as are leggings. Leggings are usually worn with ballet style flats while tights are often paired with boots...but can also be worn with shoes, of course!
If the khaki is of the green variety, I love the ideas of wearing black tights or leggings, black shoes, and black accessories (belt, bag). If the khaki is light beige, it's trickier to bring it into the fall. I would recommend brown tights or leggings with brown shoes and accessories but you can also have more fun by using color...rust, olive, dusty blue...so long as your top incorporates your leg color!
Be consistent with your accessories...brown belt, shoes and bag, for example. If the color is closer to camel, you can wear darker leg colors including black but I would avoid black if it's the truly light version of khaki!
You don't mention what night the wedding reception is being held so I'm going to guess it's probably on Saturday, but could be Sunday. Sunday allows for more casualness, by the way! You can wear any of the above so long as it's on the dressy side.
A pretty dress with wrap could be great but so could a dressy suit with either pants or a skirt worn with a sexy camisole under the jacket. If the wedding is in NYC then you will not have a problem with going to any store and finding something that you will like.
Most of the stores prizes are with in your price range...very trendy stuff as well as classics. Check out the Ruffe dress by Nanette Lepore for $190. Also, the Jersey knee dress and the CDC Slip dress.. Discounts go up to 75% off on designer clothes if you go to the right store or on the right day is when you will hit the jack pot. You might get incredibly lucky here!
Feel free to go with any color except white. Black is no longer taboo for weddings. Colors for the fall are muted and sophisticated in addition to black being hugely popular. By way of follow-up, go to any web site and look at evening cocktail dresses. Max Azria has some great dresses in your price range. There are lots and lots of websites out there which carry tutorials on resizing jeans and t-shirts. As a general rule of thumb, flip the garment inside out, place over it one which already has the shape you want, then draw along the outside edge of the well-fitting one with chalk. Cut away most of the excess, leaving an inch or so for later adjustments, sew a neat seam and turn the right way out again.
With regards to getting a more individual look I'll say what I say to everyone: don't be bound by the limits of 'alternative' shops. Pick up odd bits you like from more generic high street chains, check out local vintage sources, DIY and look in charity shops.
