Interesting. The shallot in the link Andy posted looks nothing like the shallots at wiki, which were said come in bunches.
If you ask me, there's too dang many onions. Unless you happen to be an onion connoisseur.
So, the recipe, which I happen to have the link to on another computer, already calls for garlic, so a touch more garlic and a little less of a sweet flavored onion should make up for a shallot, from what I am understanding.
This all has been a big help. No sense buying shallots, which I read are pricey in the US, if there are so many widely accepted substitutions, especially since it will be mixed in with a bunch of other stuff (it's a chimichurri (sp?) recipe).