After dialing unsuccessfully through Lowes' call-waiting system, and talking to a Home Depot customer service person who actually went into the back to see if Home Depot carries the correct replacement size (they do not), I finally got through to a Live Person in the Lowe's Appliance Department, who sent me over to the Parts Department, because the filters were not in stock in that store either.
I told the parts guy what I was looking for, and he inquired mildly: "Have you tried cleaning them?"
"Ah...Well, no," I said, "actually, I haven't, because they're literally dripping grease onto the burners - they are SUPER gross! So I wanted to get some new ones."
"That stuff should come off," the man told me. "What my wife does is, once a week she takes the filters and soaks them in a bowl with a quarter cup of Dawn dish soap. The grease just floats right off that way."
"Really? Even when they're super disgusting?!" I felt a prickle of annoyance. If _this_ man's wife could clean the range hood filters, so could Jeff Amaral's wife! "You think it would work even with really, REALLY gross ones?"
"Well, you might have to soak them overnight, or do it a couple of times. My wife does it once a week."
And gosh darn it, even though I felt like I was performing a scented, soapy satire of Jo March from "Little Women," it turns out that Domestic Goddess' Husband's advice saved us about $60 - AND substantially reduced our risk of grease fire.
However, I will tell you right now that I am NOT committing to doing this chore once per week.