You're only talking about a few months. That's nothing when it comes to rust. Like a few others have said, just scrape what you can off and go through a few reseasoning cycles and get back to cooking. Screw all the oven cleaner and other chemicals as you're just making it more troublesome than it needs to be.
I've neglected grates on occasion for a year or two and while nasty looking, they were still just fine with some good abrasive scrubbing and reseasoning. And the grates don't have to be perfectly black, glossy, and seasoned to cook food. Sure, you want all the loose rust off, but even if they are still discolored a bit after cleaning a reseasoning, they are fine to cook on and it won't take long for them to get back to normal.