iPhone 6 will be available on 19th September, 2014.

iphone6
iPhone 6 was announced on 9th September along with iPhone 6 Plus and the smart watch. It will be available for you to buy from stores and carriers by September 19th, 2014.
Here is the official price of it from the Apple Inc.
16GB     $199
64GB     $299
128GB     $399
Two year carrier contract is required.
This device will accept only Nano SIM card and compatible with the micro SIM cards.
Don’t forget to get the AppleCare+ during the checkout process for your iPhone as you will get coverage for two years from the original purchase date of your iPhone and adds up to two incidents of accidental damage coverage.

How much is my old iPhone 5S will get for trade in programs?
It can fetch up to US $300 in some trade in web sites.

Mean while there are hot news going in the internet that one of American carrier Verizon Wireless is ready to offer a Free iPhone 6 16GB version.
So what will be their conditions to get the device through this program?
It is said that you must hand over them your functioning iPhone and you will be required to sign a two year contract with them.

Read more.
http://www.inquisitr.com/1465635/verizon-wireless-offers-iphone-6-free-trade-in-deal-but-how-are-sprint-and-t-mobile-competing/
http://money.cnn.com/2014/09/09/technology/mobile/verizon-iphone-6/

Image Courtesy: Apple Inc.