As has already been said, the only way round the duty thing is for the seller to put a low value on the front of the package, a few dollars.
Also if it`s sent insured with the full value on the front, customs take great interest and tend to keep it for a few weeks and dont inform you that they have it. You wont know whats happened to it till it arrives.....It`s happened to me twice..the records arrived a month after posting, you also the added joy of paying loads of duty, as you`ve already found out.....believe me this is no good for your sleeping patern.
For dearer items I ask the seller for International Express Delivery with a low value on the front of the package. It can be tracked and will arrive a few days later....it`s a touch more expensive $20 to $30 but I think worth it.
hope this helps,
Andy