[cypher]

You could try threading cardboard through the metal of the wheel, not sure how long it would last but it might work if only as a temporary measure & would be better than it is now, don't use tape anywhere hams can get to it as it can be chewed & would be dangerous if ingested.
How much it would cost to order wheels online will depend on where you are.
Which food are you using to feed them?
Peanuts are fine as a treat, it's best to give monkey nuts (peanuts in the shell) if you can, just make a tiny hole in each end of the shell then let them work to get at the nut inside, I give mine one a week usually.
Sunflower seeds (in the shell) are fine in moderation.You can also give pumpkin, hemp & flax seeds, a few oat flakes are often enjoyed as a healthy treat too & they generally love millet & mealworms.
There are lots of veg you can give them, try to stick to the less sweet green veg for Mu, if you're not sure which veg are safe just ask.
Bin cages should be fine for them & I'm sure Mu will love the sand digging area, both should have some sand in the cage to help keep their coats in good condition.