Those bells are safe as they don't pose an immediate danger to your budgie's physical health. To be 100% safe, you would have to know which material the bells are made of and if you see your budgie licking the surface of any of the bells it would be best to replace them for stainless steel ones, as these are completely safe.
At the first signs of rust, the bells should be replaced for new ones.
RIP sweet Tito (Summer 2008 - January 17th 2013).
You are missed and never will be forgotten.