My favorite is the $13 Soundmagic ES18. I have many earphones that were under $50 each, however this is my favorite. It sounds very natural, and has good bass that sounds natural and is not exaggerated. It has nice detail. Some of the others I have either are lacking in midrange detail, or don’t have enough bass.
When I am active and need to hear my surroundings, I use the JVC HA-EB75 earphones with ear hooks. This has good midrange and treble for the price, but is bass deficient. When I boost the bass on my player by 8 db though, these are good enough for casual listening while I am active. This is under $10
Both of these also come in a version with a mic and phone control for around $3 or $4 extra.