These two are my favourite "cheats" websites.
This first one sends you emails of all the clothes that come into the sales in your size and from the websites that your interested in.
It's great you can chose both the designers and online stores that you like and does all the sifting though their sales to find the pieces that are in your size!
This next one is brilliant, it allows you to hire dresses, that lets be honest you could never afford to buy outright, for special events, interviews, all sorts.
A word of warning though! To avoid being disappointed email them with your dress choices before paying because I've found on a few occasions that they don't have your choice for the date you want!