The costs should not be published as far as i can see if the calculated costs are zero.  All cost updates have a conditional check to avoid updates where the calculated costs is zero, like:

if (cost)
   wu->setStatistic(...)

You may see the cost showing up as zero because the cost is calculated and stored to 6 decimal places but displayed to 2 decimal places (or the number of decimal places appropriate for the locale).  When the cost is calculated & stored as a value less then 0.005,   it is will show in ECL Watch or by wutool as a cost value of 0.00.