You can create a variable and set it with a Set Arg/Variable widget. You fetch the StdCost in the expression like:
with the expression:
Db.PartCost.Where( r =>r.Company == callContextClient.CurrentCompany && r.PartNum == ttJobHeadRow.PartNum).Select( r =>r.StdMaterialCost).DefaultIfEmpty(0).FirstOrDefault()
You might need to make it the sum of the various PartCost fields related to Std cost
Db.PartCost.Where( r =>r.Company == callContextClient.CurrentCompany && r.PartNum == ttJobHeadRow.PartNum).Select( r =>r.StdMaterialCost).DefaultIfEmpty(0).FirstOrDefault()
+ Db.PartCost.Where( r =>r.Company == callContextClient.CurrentCompany && r.PartNum == ttJobHeadRow.PartNum).Select( r =>r.StdLaborCost).DefaultIfEmpty(0).FirstOrDefault()
+ Db.PartCost.Where( r =>r.Company == callContextClient.CurrentCompany && r.PartNum == ttJobHeadRow.PartNum).Select( r =>r.StdBurdenCost).DefaultIfEmpty(0).FirstOrDefault()
+ ... and for StdSubContCost
+ ... and for StdMtlBurCost
The have your condition use that variable to see if it is <= 0