In that case, you might as well have my best find from Europe - expedia.com will give you about $1,190 from Frankfurt (via ZRH), out on 14Dec back 4Jan. (Options from AMS are more expensive, and I think SEA-FRA will be cheaper than SEA-AMS).

If you want non-stop it's ~$1475, or if it fits with your plans FRA-JNB,CPT-FRA nonstop is ~$1,120 on the same dates. SEA-FRA, to tie-in is about $500-600.

Editted to add: the "via ZRH" option is a similar price from Dusseldorf, seeing as it's closer to AMS, and actually it seems SEA-AMS is cheaper at ~$500.