I can only partially answer your question, Tiao. When I once ordered 2 50-pk Ritek Ridata DVD-R 8x spindles from Meritline.com, they would have charged about $9.39 in shipping from California to here in Texas. Amazon would have charged me about $6.52 for the Verbatim 8x DVD+R 100 pk spindle I ordered from them.
Wait...I found a small scale to weigh them.
50 pk spindle would weigh about 1 lb. 12 ozs.;
100 pk spindle 3 lbs., 6 ozs.