FineTech007 via eBay offers this Mini Stereo Microphone for Smartphones for $2.24 with free shipping. That's tied with our April mention and the lowest total price we could find by $4, outside of other eBay sellers. It connects via a 3.5mm jack and records volumes up to 110dB. The microphone features a tilt-up mechanism to reduce contact interference.
Note: This item ships from mainland China and may take three to eight weeks to arrive.