Soyee,
I also ask the same question 2 month ago!
I rec'd the answer from one Bk mami here, she told me the price is so difference is because different clinic choose different "brand" of the vaccine and she also told me the best is "Glaxo Smith".
The clinic I went choose the above brand and it cost $450.
My daughter had no side-effect after that but I feel this injection is more painful than the other inject (like:3mos old / 1yr old vaccine inject), because this chicken pox vaccine is need to inject under the skin not the muscle as I understand.