Yeah, sandblasting will take off EVERYTHING, instantly.
Check your local listings for a sandblasting company. I've had them do a whole 55 gallon drum, inside and out, lid and all for only $25.
Just be aware that you'll end up with raw, bare metal and it will start to rust very quickly when exposed to air or moisture. Just spray the grates down with veg oil when you get them home, then heat to season.
Big JT's Smokin' BBQ Competition Team
"Oh, I donít reject Christ. I love Christ. Itís just that so many of you Christians are so unlike Christ."