How can I make a rusted cupcake pan usable again?

I wouldnt try to clean them, use as a decor. Paint the bottoms with flowers or even put dried flowers in them, paint snowman, when finished, hand on wall

You can wash it, then sprinkle with baking soda and scrub in small circular motions to remove rust. A scouring pad works best. Rinse again, let it dry, then coat with cooking oil to prevent further rust. If the rust is deep in the pan, it is probably best to retire it for baking.

You could try using vegetable oil to get rid of the rust.

Comet cleanser and scrubber sponge then wash with hot water and Dawn dish soap---Steel wool---Aluminum foil use like steel wool use cupcake or muffin papers or silicone liners for easier care also hand wash do not put in dishwasher it turns metal black/gray oxidation