A long (ankle length) floaty dress with a pashmina. Look on eBay if you are really broke!
Good luck!

There is no shame in wearing a trouser suit to a wedding, as long as you get the accessories right. Choose a summery colour - a pastel perhaps - and wear with a silky camisole, a corsage (very fashionable this season) and high heels. Look for high-waisted trousers and a fitted jacket. You should find something perfect at Wallis, Windsmoor - and M&S is always reliable for decent tailoring on a budget.