Looking for a cheap unlocked (Windows) phone

Hi Everyone,

I am looking for a cheap unlocked phone that will be able to run WP8.1 when it is released. My iPhone 3GS just broke and I am looking for an upgrade that won't break the bank but will be good enough for me to enjoy using.

I don't mind purchasing used in good condition if it will get me a better phone for much less. If by any miracle the phone you want to recommend is also rugged/waterproof/lifeproof that would be awesome (but not necessary). Good battery life is important to me.

Here's to hoping I'll be joining the WP family soon,