Hi. @Sun Jiang
Most Telcos shops may have this Xiaomi Redmi Note 3, as it is not that popular as iPhone.
Phone price is around $300, which depend on the storage &or RAM.
Do note that the actual model is Xiaomi Redmi Note 3.
Because there is another model "Mi Note", which sound familiar.
I have is the Xiaomi Redmi Note 2.
Battery is excellent & long lasting.
Do note that there is NO Xiaomi Sales shops in Singapore.
If you did by chance a Xiaomi shop, it is not from Xiaomi and no warranty for it, as it may be export handset.
But there is this Xiaomi Service Center shop in Central MRT.
Getting from Telcos is safer, and also available from Challenger, with 1 to 1 exchange within 1 week for problems.