Corn Silage Yield estimates with our spreadsheets (http://www.das.psu.edu/dairy-alliance/xls/pricingstandingcornforsilage-revised.xlsx ) this fall, we (Tim Beck, Virginia Ishler and I) found that the price depends on where you are measuring it at. At $7.00/bushel corn and a delivered price of $75.00, corn standing in the field was worth about $45/ton in one of our scenarios. According to the NASS Custom Rates (http://www.nass.usda.gov/Statistics_by_State/Pennsylvania/Publications/Machinery_Custom_Rates/custom11.pdf) it costs about $9.60 a ton to chop haul and fill silo, so its worth about $55/ton in the silo, before its fermented.
These are close to the old rule of thumb estimates that corn silage is worth 8-10 times the value of shelled corn. I suspect the range is somewhat due to where you are measuring it.