The number and cost is on Sony's website. would have taken you less time to browse to sony.com.sg than post this thread.
Here's a BIG hint:
1. go to www.sony.com.sg
2. Put your mouse over "Support".
3. Look! There's a link called "Service Charges".
(see how easy it is when you apply some logic?)
They will NOT clean dust if it's only a little bit (dust is normal), but if it's fungus and they need to clean it, they may charge you very little if it's in an easily accessible part of the lens, or the full servicing fee if it's in a sealed part of the lens.