Budget in a 32GB uSD Card once you are satisfied with CZ + M2 or CZ + M3?
You may need to up the budget a little bit if you want something better. And most probably, you'd need to get them new from overseas or used from head-fi which involves shipping + customs.
I'd agree with #[member='vantheman5211']. It really depends on what you want. Of the top of my head....
Technically speaking, RE0 / RE-ZERO are upgrades, but I can safely rule them out if you are looking for M2 kind of signature. You could look at Etymotic HF2/3/5 if you are looking for RE0 kind of signature (bass light, but great clarity and details, good mid range and treble). Phonak PFE is a good choice, but then it has gone up to $180 in recent times. DBA02 MKII is another good choice. But, I suppose you are not looking for this kind of signature.
I'd consider JVC FXT90 - if you are ok with just good bass and colored sound. Of course, there's the TF10 which can give you a thick, fun sound but with little of that BA speed as well.
EX600 can be considered as a good choice which can do all three ranges well, but the bass and treble are not as refined as EX1000 from what I read. It should give you very good sound stage, even better than FXT90.
If you want a fatigue free signature, Fischer Tandem can do it, though I feel about $100 is the maximum I'd like to pay.
RE262 is a mid centric choice, but does well with respect to sound stage and will require an amp to extract the last mile of performance.
