My daypack is the North Face Solaris 35.
http://www.thenorthface.com/catalog/...olaris-35.html
It's actually a little excessive for most day hikes but it is great. It's about the price you're looking for, will last damn near forever - I've used mine for everything from day hikes, bike rides and air travel for about five years or so and it is still in almost perfect condition. Actually I just need to figure out how to clean it! I'd definitely recommend it though.