TomTop offers this Magnetic Putty in several colors (Black pictured) for $2.99. Coupon code "TTPU34CX" cuts that price to $1.97. With free shipping, that's $2 off and the lowest price we could find. It can be stretched and bounced like rubber, sculpted like clay, and torn and ripped like paper.
Note: This item ships from China and requires 10 to 20 business days for delivery.
Looking for additional cash? Here are a ton of options that are accessible to anyone with internet access.