oven cleaner?

They'll never go back to shiny like-new condition, but they might be usable. And they are pretty cheap, you can get them at WalMart for about $8 each.

One way to clean oven racks might work, altho I can't predict if aluminum might react while steel won't. For oven ranks, place in large black plastic trash bag (I'd do cookie sheets one at a time, can't stack them for this method). Lay bag with pan flat in an out-of the way spot to be undisturbed for at least 24 hours. Then pour about 1/2 cup of ammonia into a cup, and place the cup UPRIGHT in bag, do not spill. Then tightly close bag for 24 hours or more. Again, no need to spill ammonia, th fumes do the job. You should be able to wash off a lot of crud after that, minimal elbow grease.

Easy to fix: Coat them heavily with spray-on oven cleaner ... tie them up in black trash bags ... and sit them out in the hot sun a few hours. Okay, this might not be the best time of year for this method, but maybe you'll get lucky and we'll have a hot afternoon. Alternately, you could put the bags in the trunk of your car (assuming your car's in the hot sun).

When you take them out, they'll clean up like new.

If they're really, really nasty, you might need to do this twice.