I bought an Epiphone Goth LP Studio from Musician's Friend via Amazon.com, just arrived yesterday.
To buy from Musician's Friend, you will need a vPost account (
http://www.vpost.com.sg). vPost will give you a US address to send your items to.
What happened with me was, I ordered the guitar from Amazon.com (I hava an Amazon account, so it makes things easier, because all my shipping and billing info is already recorded), where Musician's Friend is a reseller. After the order, you can track your package through Amazon, and Musician's Friend will also email you once the item is delivered to your US address (delivery from US is free after a certain amount ordered from Musician's Friend, Amazon charges about US$20). Once delivered to the US address, you need to pay the shipping charges at vPost, then you can track your package from the vPost website.
My guitar was ordered on 24th March, delivered to the US address 30th March, arrived 10 April.
After adding up the costs (guitar + shipping + vPost insurance charges), the guitar is about SGD$100+ cheaper than SL!
Shipping charges are at SGD$12.99 for the first kilogram, SGD$8.99 for each subsequent kilogram. So you can estimate your shipping cost if you know the weight of your item. Books, CDs and DVDs have a different shipping price system. But it's likely you won't be able to bring in amps, because speakers are listed as a prohibited item to Singapore.