Sunsmile*2013 via eBay offers the Mini Stereo Microphone for Smartphones for $2.75 with free shipping. That's tied with our mention from two weeks ago and the lowest total price we could find for such a microphone by $3. It connects via a 3.5mm jack and records volumes up to 110dB.
Note: This item ships from mainland China and may take three to eight weeks to arrive. It may also be missing its original packaging.