For $20 or less, I'd definitely go for the CX300 over the MMs. I got the MMs on clearance from CC for $8 when JVC decided to change the MM's packaging design. MMs for $8, yes; for $19, I'd pass on it.
Hope the DE earphones work out for you! If not, there's a lot more sub-$20 earphones to try.
26.2 | 13.1
+ Quantum Conundrum
+ LittleBigPlanet 2
Far Cry 3