If I may suggest an unorthodox idea? Buy an old smartphone (preferably Android based, not sure if the iphones have flac support). Get one that has an microSD card slot so that you can upgrade/add more storage if it's built in memory is insufficient.
You can also find many free music players in the Android app store if the Android smartphone that you buy doesn't have native support for flac.
Here's a sample article that could help: http://www.talkandroid.com/guides/beginner/breathe-new-life-into-that-old-android-phone-by-turning-it-into-an-personal-media-player/
You could find a used smartphone that someone's selling cheap.
As for durability: Find a case for it.
Added bonus: if you get a model with wifi (almost all of them have that) than you can do some casual web browsing when near a hotspot.