I have a perfume-bottle-sized aceto tradizionale reggio emilio, which is delicious, but when it's gone I won't even consider replacing it. It probably goes for over $100 now, while I can get a 375ml bottle of Pedro Ximinez sherry vinegar for around $17. The sherry vinegar is a little dryer, and not quite as viscous, and has a different flavor profile. But it's every bit as good, and at least as complex, and I don't feel like I'm dispensing some irreplaceable elixir every time I throw together a vinaigrette. What's more, for 1/3 the price of that precious balsamico, I've put together a whole stable of sherry vinegars from Despaña in NYC, that includes moscatel, fino palomino, and cheaper grade palomino vinegar in a big bottle. In my vinegar cabinet, Spain has ignominiously kicked Italy's ass.
Edited to add: I don't like the supermarket grade balsamic vinegars. I don't know what they actually are, or why they get so much shelf space.
