With orders of $25 or more, Amazon offers the Nickelodeon Teenage Mutant Ninja Turtles Microphone for $5.97 with free shipping. (Walmart has it for the same with free in-store pickup.) That's $9 off list and the lowest price we could find. It requires three AAA batteries (not included).

Note: This item is part of Amazon's "add-on program" and can only be purchased with orders of $25 or more.