A friend of mine found her wedding dress at a sample sale over the weekend. She had to decide between two wedding dresses that she loved. One dress was a little too big and had to be taken in. The other was a little too small and had to be let out.
She went with the one that was a little too big, because it would be easier to take it in than to let the other one out.
When you're buying your wedding dress, whether at a sample sale or off the rack, it's important to think about not just the cost of alterations but the amount of work needed on the dress. For a dress with a lot of beading the seamstress will have to take off the beads, take in or let out the dress and then re-sew all the beads, which will cost you a lot more than a simple hem.
Also, if a dress is so big or really too small the look of the dress may be completely different after it's altered. My sample sale wedding dress was a size 10. By the time the seamstress was done shortening it for my size 2 frame I lost so many inches off the dress that a lot of the detail I loved was cut off.
Think about the work the dress will need because it may add a significant amount to your dress budget. And if you can, talk to a seamstress at the sale or store to see what work can be done to the dress to ensure that it will look the way you want it to on your wedding day.