if the brown bits have not disappeared, then I would have the feet checked. Have a look at the links I have given you so you can see what you need to look out for. Bumblefoot usually starts with localised red spots. If the pads are all read, it is either warm feet or slightly sore feet.
You could look for second-hand rabbit cages on your local free-ads. They should be much cheaper and definitely cheaper than any vet care for bumblefoot! You can bring a second-hand cage back to a good state with a disinfectant and or or two soaks of warm white vinegar for the stains, plus some energetic scrubbing. Perhaps you parents are more accessible to that idea?