Tell you a novel approach, if you want a formal look with a low price tag, is to treat the bridesmaid dresses as essentially disposable, and therefore buy the cheapest ones that the 'maids will agree to wear.

Like theatrical costumes, bridesmaid dresses are mostly seen from a distance, so shoddy workmanship won't show. Unlike theatrical costumes, bridesmaid dresses don't have to stand up to vigorous dancing and singing (we hope!), so it's unlikely that the dresses will fall apart mid-wedding.

Though this is a story in Bridal Bargains about a maid-of-honor's dress that did come apart at the seams during the ceremony!

If your reception calls for dancing until dawn, it might be wise to encourage bridesmaids wearing little cheapies to bring a second outfit (and they may feel prettier, too).