Below is a summary of my charges.
Service Fee:
1 item = 11%
more than 1 items = 11% for the first item (highest value of all items) and 8% for additional items
Shipping Charges:
1st item = US$25
additional single item in one shipment = US$20
additional multiple items (value less than S$400) in one shipment = US$35
I will try to ship the items in 1 combine shipment. However under Singapore Customs regulation, all packages that has a value (declared value + shipping charges) more than S$400, the receiver will need to pay for Singapore 7% GST of the total value of the package.
http://www.customs.gov.sg