Richard, it does take patience and practice to clean up the wire racks and cooking grates without doing the angle grinder dance for sure.
That is what I would do. You still won't get them `100% clean of rust as there will be spots on the cross welds you just cannot get to. Otherwise, you can just knock off the loose paint and rust and do what BPratt suggests.
After I grind as much of the rust off as possible, I give it a good coat or two of Rustoleum rust reformer before I spray them Rustoleum 2x gloss or semi gloss black.
But, in reality, neither is a real good solution in my opinion. If you can find one from a donor grill that is in better shape, I would go that route. I currently have one on my personal grill that is in rough shape, but it will be replaced with one from a donor grill as soon as I come across one. It is one of the longer ones for the Silver C type frames so they are less common than a silver B. So, it may take a while.
Otherwise, you can always fab in a bottom shelf something like this:
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