Enabling my yarn addiction

I lead a fairly boring life. When you get right down to it, so does most of the family. Even the ones who may have been a bit wild in the past now have respectable jobs, like being a substance abuse counselor.
The extended family does a Christmas gift exchange. Pick a relative's name out of a hat, get them a gift. You know the drill.
A couple of weeks ago, my brother in law announced that he'd gotten my name and asked me what I wanted for Christmas. I suggested a gift certificate to a local yarn store.
Then he had to ask the fateful question: "How much money do you want on it?"
Trying to be polite, I hemmed and hawed. But he persisted in wanting to know a specific dollar amount.
My sister in law knits, so I appealed to her better judgement. "Would you explain to your beloved why it's a bad idea to ask a knitter how much money they need for yarn?"
Since their household has close to 25 years worth of collective sobriety, she chose a metaphor that would be easily understood. "Baby, when you were on dope, how much of your income did you spend on it?"