Sentence:  Despite this danger , however , we are informed on every hand that ideas , not machines , are our finest tools ; they are priceless even though they cannot be recorded on a ledger page ; they are the most valuable of commodities - and the most salable , for their <WSD>demand</WSD> far exceeds supply . 
Meaning of the word marked with <WSD> tags:  the ability and desire to purchase goods and services