I don't know about their more up-to-date models, but Sennheiser's MX range have always struck me as great value for money, in terms of SQ.
You should browse Head-Fi and see their reviews, that's all they do and it's great for that BUT, careful because dedicated forums have a lot of bias.
Anyway, all I am saying is I have tested $20 and $2000 headphones and my favorites are all between $50 and $200.
what are your favorites IEMs in the 50-100$ price range?
Well, I gave those away, I didn't like them at all. You can try cheap ones but you still have to try great grands.
Did you check that link I sent you? They have good headphones for all prices.
I've decided I'll try a very cheap model which should also be decent and, if I'm not satisfied with that, I'll switch to a pricier one.
I keep looking worthy upgrades to my favorites Sony MH1 and LG Quadbeat 3. They costed me about 15$ each.