Looking for furnished flat for the summer

I'm a 34 year old American, non-smoking man, and I am coming to spend the summer in Berlin. I'm very tidy and very respectful, and can give references so you know that I'm trustworthy and reliable. I would like to find a decently priced flat (under 450-500 including utilities) for the three months I will be there. I arrive May 16 and will leave at the end of August, so a June through August sublet would be ideal (I"m flexible). I am looking for a furnished place with a kitchen that has wifi/internet (this is a must, since I work online and don't want to spend every day in a coffee shop!). I would consider a flatshare if it's not with a student (unless they're older) and just one other person (no preference for gender, but you should be gay-friendly). And of course I'd love to be in the Kreutzberg or Neukoln areas! If you have something available, please let me know! I'm in the states until I arrive next month, but we can communicate over email/skype/whatsapp.