EXK cost for Ag are under ten bucks an ounce because of all the gold they produce, they are producing around 15k Au oz per quarter, so conservatively that's about $20 M each quarter, and at some point PM prices will start moving up, and it's OK if it takes awhile, because the wheels will start to fall off before PM prices start to move higher, that's what happened in 2008-9, and it will probably play out that way again
if you can't take the volatility and manipulation, then wait til earnings are announce to sell, because we probably bounce 10% on that day, and it's coming soon
A rough swag answer to your question: 2012 Revs were 208M and net earnings from operations were 42M. 42M divided by 208M gives you a net profit margin of 20%. The average spot price of silver for 2012 was roughly $29. Applying the 20% profit margin to the average spot price of $29 ($29 * 0.8) gives you a rough cost for silver production at $23, about where we are trading now. But you need to factor in higher revs with improved efficiencies and higher yields on gold per ton mined. My guess, EXK breakeven point is closer to $20 per ounce. Sustained spot prices below $20 will likely cause pain, and sustained prices at current levels will impact margins, but I think we can still count on nice increases in revenue and a profit if we hold low 20s or better.