RE0 does need an amp to shine.
RE-ZERO can be considered, but it's different from RE0 - slightly better bass texture, but not different in terms of quantity, smoother and relatively forward mid range, relatively laid-back but still sparkling treble. I also found RE-ZERO's layering and presentation to be better than RE0. RE-ZERO can sound a tad dry and RE0 can sound a bit thin, vocals could be unsatisfying. They should be more in the mold of PL30 than M2. Of the two, you are slightly better off with RE0 + Amp for Rock.
You can also take a look at Etymotic HF2/3/5, whichever can be had for less - new or used. They essentially are the same, except for mic variations. HF2 I have is better built than the RE0 I had, though the later versions of RE0/ZERO had thicker cables. Looks wise, I prefer HF2 too. There are a few issues with HF2 namely the requirement of deeper insertion with tri-flanges (which takes a bit of time to adjust and even then could scare you every now and then by bring out bits of ear wax you never thought you had out with it
). The sound stage and bass quantity on the Ety are almost non-existent. Yet, once you get past all that, it's an enjoyable IEM for it's mid range, detail and treble presentation and of course, isolation once you get the fit right.
TF10 would be more fun sounding than any of the three I've mentioned.