Without the ability to use the phone on most wireless networks what you have is an iPod Touch. You can buy a new iPod Touch, one based on the iPhone 5, for $229. No cracks, comes with a charger, speaker works, etc. For $300 you can get a 32GB one.
Last week my sister bought a 16GB 4S from the Sprint store for $150 to replace the one that someone stole from her. My iPhone 5 32GB was only $300, with a contract of course, but it also came with a charger and has no cracks.
I would say your phone is worth maybe $40.