I've never heard it quite like that. In my experience, the usual expression is "WHAT I wouldn't give for..." The word "what" is rhetorical here; it means that you would give (pay, trade) almost anything in exchange for the thing you want. ("What wouldn't I give for [X]" = "there is almost nothing I wouldn't give for [X].") It's usually an exaggeration. What the speaker really means is just "I really wish I had [a few samples of that dust]."

You forgot one keyword.. WHAT I wouldn't give.. What I wouldn't give to be rich and famous. What I wouldn't give to finally be fluent in Spanish! What I wouldn't give to win the lottery. What I wouldn't give to go on a date with her! It used when expressing your desires and what you long for. It means you want this thing SO MUCH that you would trade anything for it. " What I wouldn't give..." It's an exaggerated fun way of expressing the idea that you are having to think really really hard about something you wouldn't trade or give up in return for this thing.