I've seen a couple of solutions:
- Dishwasher paint, like Uber Goop
- Vinyl paint
But some reviews of some of the "paint" products say it doesn't last long. If this is only a temporary repair it might be best just to get another rack for $100 or so (rather than spending $10 and an hour to just have to repeat it in a month.
Also someone recommended running lemonade (unsweetened mix packets) through the dishwasher to initially remove the rust.