Let's look at the GST first, which is 7% of CIF. CIF includes the purchase price of the bottle plus shipping all the way into Singapore. Let's assume the shipping (incl. any insurance, if applicable) is S$25 (S$10 to Comgateway and S$15 from Comgateway to Singapore) and the bottle is S$47.50 (35 USD converted to Singapore dollars). So that's S$72.50 * 0.07 = S$5.08 GST.
OK, now the alcohol content. The excise duty is S$88 per liter of alcohol. A 750 ml bottle at 40% alcohol contains 300 ml of alcohol. 300 / 1000 * S$88 = S$26.40.
Adding it all together:
S$47.50 bottle
S$25.00 shipping (whole journey)
S$5.08 GST
S$26.40 alcohol duty
= S$103.98
That's more than double the original U.S. dollar cost in this example. Or you can just use the Singapore Wine Vault's handy
online calculator.