Balsamic vinegar is a lot like wine - you can get a decent bottle for a reasonable price, but at the high/old end, it gets exponentially more expensive. The $1000 a bottle stuff isn't something you'll see at a normal retailer - I think you need private appointments to get near the stuff.
Balsamic is great in salad dressings too, when used in moderation. I've had a great balsamic-soy dressing with a spinach salad, for example.