Can't compare iPhone to the Sony. They are made of completely different materials. Sony a17 is all plastic. I just paid $300 for a music player, I would prefer it not be scratched within one day of it being in my pocket. Asking for a case from the store where you bought it is not a lot to ask. All kinds of schiit can get in your pocket. Might mistakenly put it in there with your keys, or a coin, or even a bit of dirt. If this thing had gorilla glass on it then I wouldn't care. a17 is extremely easy to scratch. I have a sansa clip as well, also made of plastic, but it's $25 so I don't really care too much about it getting marked up a bit.
Dude, I just told you there are no links to buying cases online. Even ebay doesn't have one. Please show me a link, and for something less than $50.