=CCur(DLookUp("[Supply_link]!supply_price","[Supply_link]","[Supply_link]!sup_number=[Forms]![SuppierOrderCreateNew]!sup_number_combo And [Supply_link]!product_number=[product_number_combo]"))
If this does:
Code:
=DLookUp("[Supply_link]!supply_price","[Supply_link]","[Supply_link]!sup_number=[Forms]![SuppierOrderCreateNew]!sup_number_combo And [Supply_link]!product_number=[product_number_combo]")