The insides of the straws are very hard to clean, and the silicone parts of the straws are starting to get a bit discolored. I think it's mostly due to the polyvisol- it's nasty stuff, so we mixed it in with a bit of juice for them. I've been looking into buying replacement straws, as everything is still in good shape, but what I've found so far is that they are just as expensive as the cups.
I've considered replacing the cups all together, though I will go with the munchkin straw cups if we go that route. They're easier to clean.

Does anyone know where you can buy cheaper replacement parts for the cups?
And how often do you replace your child's cups?