I have some Futuresonics Atrio M5 in-canals, which were about £80 (I think they're less than $150 in the US), and they're incredibly good. Comfortable, and very good sound quality - deep, but tight/controlled bass, accurate and not harsh mids, and good quality highs. Also look good and unobtrusive.
I took them, along with my iPhone earbuds, to my friend who runs an audio repair shop, and he fixed them to the iPhone cable/button for me. It took him less than 10 minutes to do a very good job, and everything works perfectly (inc. button/mic).
All you need to do is chop the wires on both, and re-solder/cover with (white) heatshrink to protect the join. If you want something totally stealth without the heatshrink visible, and arguably more secure, you could either fix a tiny jack plug onto the bottom of each earbud and the cable ends, or take apart each casing and resolder directly inside the bud itself (taking a lot more time, effort, and more potential to muck things up).
Ultimate Buds also do a similar thing with a couple of models of earphones.
If you don't want to be bothered with all this, then you could always just get the Shure adaptor and some normal earbuds that you like, some of the Ultimate Buds, or V-modas etc.