If you found M2s bass very heavy for your taste and are looking for something with lighter bass , the options I can think of are RE-0 / RE-Zero and a Brainwavz M3. But none of these , have a soundstage as wide as the PL-50 .PL-50 has some exceptionally wide soundstage for an IEM under 100$ .You would find something that good or better only in an RE1. RE-1's true potential can be unleashed only if you amp it well .So that cant be considered as an option right now .Also RE-1 has its own drawbacks like lack of treble etc so we cant be sure if you will like it after spending on the amp as well.
Between the RE-0 and RE-zero.. the RE-0 needs a decent amount of amping, even a Fiio E5 shows some results. But even without an amp they sound fairly well unless you need lot of volume but most important thing is the unique sound-signature . The RE-0 - you will either love it or hate it .They have a very dry , neutral and analytical sound.The bass is light enough to just give you a light punch once in a while (better with amp -but only midbass ) .The mids are amazingly detailed , you can hear things you might not have heard before but the midrange is again a little dry and lacks that slight warmth in sound which gives it a life and makes it musical. The treble is by far one of the best ever in a universal IEMs. Very well extended and insane amount of micro detailing , transparency in sound .If you love your treble it surely makes you go wow ! :O
The RE-Zero (haven't tried) but is supposed to have similar sound from what Ive read with slightly more refined treble and mids .Also since its low impedance it doesnt need any amping at all.
Now coming to Brainwavz M3 , its one IEM which strikes a perfect balance between neutrality and musical sound .Its not as dry or analytical as the RE-0 but it isn't as bassy or warm as the M2 as well.Everything is perfectly balanced . The bass is light/medium in quantity but has a very nice deep sub bass .No heavy rumbling impacts like the M2.The mids are more clear and have an openness compared to M2 but they dont have the aggressiveness / congested warmth of M2.M2s mids sounded like a rush of instruments and vocals whereas the M3s mids sound more smoother and clear. The treble is also slightly better than M2 but I really cant recollect much about it so could be wrong .Would be best if you can read Brendon's impressions in this thread on the M3 .
http://www.techenclave.com/audio-zone/brainwavz-m3-is-here-176936-2.html
The M3 currently looks like the perfect buy for you if the 79$ preorder price is still on, only thing I would be worried about is the fit/isolation. If you didn't get a good fit or isolation from M2 its possible you would face similar issues with M3 as both have same eartips and nozzle structure. Other than that M3 is definitely more VFM and a better option than an unamped RE-0.
Just go through a few more reviews of the possible options under your price range.I might have missed out something . Read more user impressions / reviews and decide based on which you find most suited for your tastes.