I built a cheapy 4 line lcd/arduino interface for my custom security system for around 60 bucks. It was butt ugly because good cases are hard to find or expensive to custom build. My wife HATED it. So I found a cheapy android (1.5) ebook with wifi and rooted it for about $90 (could probably find it for 60 now) and wrote an android app. It looks WAY better than my butt ugly lcd and is also going to be an interface to my weather station (when I get around to finishing it) and a few other home automation projects.
The really nice thing about the whole thing was that when the company I am working for decided to develop a mobile app, my boss (who knew I had done the android security interface) threw the project to me. Android apps are pretty fun.