That $150 LED panel you're talking about is unlikely to be IPS and will probably be a TN panel with terrible viewing angles. They're not the same. And there is a cost worthy benefit to some people to have an all-in-one design encased in aluminum and not black plastic. I'm not saying the Mac Mini is a bad choice for the OP, but just wanted to not dismiss "a monitor" as just a monitor. It's really the visual lifeblood of your computing experience.
I think you need to give a look at the IPS section of a major retailer like BestBuy.com (not the best retailer by any stretch, but they sure have a wide range of everything); there are currently 13 IPS LED monitors from major brands available in the $100-150 bracket alone (those are just the IPS models, I filtered out the non-IPS stuff and everything above $150).
While I know not all IPS LED monitors are created equal and there's no guarantee they're as good or better than the iMac display (which is made by LG anyway), there are many decent options out there.