IPHONE 5C. Which one to buy in ebay us website to use in India?

I'm (from hyderabad, India) a tech freak, want to own/buy a iphone 5c.one of my friend is coming from usa in December first week. So i have decided to order/buy a iphone5c on ebay us(united states) website. I'm very much confused on which mobile to buy. Even my friend doesn't know.
there are 4 types of mobile networks are there in ebay us website.AT&T, T MOBILE, VERIZON AND SPRINT. Forget about unlocked devices (becos ranging around 600$)
AT&T, T MOB are gsm networks… Rest are cdma.
AT&T mobile are ranging aroung 400$
My questions:
1) which mobile i have to buy/choose & can unlock easily in India to use Indian gsm networks(economically)?
2) please tell/suggest me how to get a iphone 5c @ best cheap price to use in india… (using ebay)
3)some of the sprnt & verizon network mobiles(less price comparatively with at&t) are having BAD ESN. If i buy this bad esn mobile can i unlock it and use in india?

Please experts please help in getting a iphone @best cheap price.

Buy from ebay iphone 5C AT&T used or new, remember better buy unlocked, because the price to unlock AT&T iphone to work sim card worldwide is from 60$ 150$. This is my suggestion.