Yuin PK2 sound great and don't isolate much and can be found for around $60. I'd definitely use those if I was in your situation.
I'd recommend Yuin's G2/G2A clip-on earphones, but they seem to have become difficult to come by. I bought mine from a seller on Ebay about 2 years ago and back then they were easy to find. They sound very good and balanced and isolate sound even worse than earbuds do. Nowadays this seems to be the only place where you can buy them: http://www.aliexpress.com/store/product/Freeshipping-YUIN-G2-In-Ear-Earphone-Headphone-HiFi-Clip-on-Headphon/908705_494777316.html
A bad thing about clip-on earphones is that they leak sound, so you might disturb your co-workers.