Its possible yes. The cost will depend on the capacity you buy.
You can check the Apple Online store for prices.
http://store.apple.com/us/buy-iphone/iphone5s
If the Carrier you wish to use it on is GSM then you can choose the T-Mobile version. That is the unlocked version for international GSM carriers You cannot buy an iPhone for international CDMA carriers
A couple of Notes:
1. The Warranty is not international, should something happen to the phone you would need to physically return it to the USA for under warranty service at an Apple Store. No mailing allowed.
2. Due to the differences in GSM bands used by international carries some features such as LTE may not work at all on the Phone.