Audio-Technica ATH-CKM50A In-ear Diaphragm Earphones for $19.95 shipped.  Here is a screenshot for your reference. The earphones feature 12.5mm rare-earth driver, gold-plated 3.5 mm stereo mini-plug, 5Hz to 24kHz frequency response, 104 dB sensitivity, and 16 ohms impedance.  Most places have them for about $39.