Unfortunately I don't know anything about their conversion rates, but it looks like they've got pretty good numbers on compete.com (http://siteanalytics.compete.com/coolmaterial.com/). Maybe someone on here knows?
Assuming 1000 piggy banks at $10/week allowance puts your monthly take at 40k. Virtually all of that money eventually gets spent.
At the lowest level of amazon commissions (4%), you're looking at $1600 per month. If you were at the highest level (8.5%), you're at $3400 per month.
It's not awesome at 1000 users, but it pays some bills.
I'm just making a suggestion - don't put all of your eggs in one basket. If you depend on one company for 100% of your revenue (Google, Paypal, Amazon etc)that's a huge risk.