I also like to buy online from US websites such as GAP, Mer & ebay. The prices for some products eg. cosmetics, may be cheaper when I buy from those US websites rather than buy from the cosmetics counter here.
One way I save on the delivery charges is to buy from a few websites about the same time so that I can consolidate my packages for shipments from USA to Singapore using vpost. I prefer to use vpost to ship my items back rather than borderlinx as vpost is so far quite fast, it takes about 1-2 weeks or slightly more to reach Singapore. I've used other courier services before but it takes longer & some of them charge GST for consolidated packages with cost (incl delivery charges etc) > about S$400. I think vpost only charge GST for each package > S$400 so I can save in this area.
When you consolidate packages to be shipped back together, you pay only 1 base charge of about S$13.40 plus the individual charges depending on the weight of the packages & size of the package or box. Eg. I bought a small Coach/Kate Spade wallet from ebay in USA, the individual charge would be about S$4-5 only if the seller send it in a small package. If I bought some T-shirts from GAP around the same time & they are packaged in a big carton box, it may cost me about S$20-35? or more. So I would have to pay S$13.40+$4+20=S$37.40 for the 2 consolidated packages for the shipping charges to vpost. If I bought 5 T-shirts from GAP & a wallet from US ebay, my shipping charges for each item would be approx. S$6.30. If you want to save more on the shipping, buy more items from same online shop to reduce the shipping cost per item.