@Terrificli -- I am no expert, but I would guess our old friends supply and demand have a lot to do with it. Balsamic vinegar isn't exactly a new innovation, but it got very popular almost overnight and everyone wanted it. Because it takes time to make that stuff, demand outstripped the supply.
Now, the supply has caught up and prices have dropped in line with it.
But, that may be only part of the picture. The other part may be that ways have been made to more efficiently mass produce balsamic vinegar. When production costs drop, sales prices tend to drop, too.
Again, all of that is only a guess, but it makes logical sense (I think). You will notice, by the way, there are some balsamic vinegars that are still very expensive. The price hasn't dropped on all of them, then.