Bluefly: Stuart Weitzman shoes are $99-$150—see their white options
J. Crew: Get an extra 30% off their final sale items with the code EXTRA30. Several long white dress options are available that would come out to just over $100 with the extra discount—perfect for a second dress if you want one.
Nordstrom: Their anniversary sale is going on now online and in stores and includes loads of great dress options for your engagement party, rehearsal dinner, bridal shower and more.