For the weight loss, depending on discipline, and what you do, you CAN push yourself into 2-3lb (fat is 3500 calories) of loss a week.
a 1500 calorie diet will passively get you around 1lb a week, but even light exercise can push you into the 3000-3500 calories a day range, and while yes, this would be up to 4lb a week +, you will rarely ever stick to a strict 1500 the whole week.
as for weight loss, doing heavy exercises with compounds, squats/bench/overhead press/row/deadlift will passively increase metabolism for upwards 36 hours, and this is on top of cardio which when you are fat, you can just walk and damn near get a cardio exercise.
from personal experience, I have changed very little about my diet, I wasn't near break even and gains were made over the course of a decade, and from the looks of it I will be coming up on around 90-100lb of loss at the year mark.
as for the dress, as others said, second hand would be hard, but think of it this way, the dress material could make several plushies, and depending on if they had them, you take the dresses which would be high class, and make them affordable by more people, you may or may not get ballpark dress equivalent prices depending on how overpriced the dress was and if it wasn't just the materials are hard to get.