You can get about $80 for a $50 bag on ebay right now, and the buyer pays shipping fees. Use a flat rate box, as it fits easily and is cheap considering the weight. You end up getting 1.6 cents per penny.
Last year it ws $130 for a $50 bag. Much better.
I think prices will go back up, so right now I am not selling. But if you need to, for space or money, then expect about $80 per $50 bag. IF you can hold, call it an investment and it should appreciate more than the average mututal fund in the next 2 - 3 years. :-)