What is the cheapest unlimited data plan?

I've been with AT&T for a long time and I'm tired of how expensive their service is. My plan is up soon, so I have decided to leave to another phone service. What I'm looking for is this:
-Free/cheap smartphone with activation
-Unlimited text and data (nothing really slow either, if I'm gonna use the internet I don't want to wait 5 minutes to use an app or load a page)
-about 300 minutes of talking (for emergencies and a talkative mom)
- Under $80/month

The ideal phone that I want is the Samsung Galaxy, but any of the newer androids are good too. I'm okay with an iPhone, but I doubt anyone is giving one of those away for cheap.

Under $80… Well that tosses out Verizon/ATT/Sprint and Tmobile… LMFAO!

you may want to go prepaid, like STriaght Talk or Virgin Mobile… But cheap = cheap… You get what you pay for

Att is expensive so I switched to T-Mobile I got an unlocked nexus 4 from Google ( which I love) for 350 dollars and a plan with T-Mobile for 30dollars including

Unlimited texts
100 min calling ( I know not 300)
5gb data ( basically unlimited but its really hard to run out its a lot, a lot more than other plans from other places when they say 'unlimited' they mean a lot I've been on this for a month and I've only used 1gb and I use data a lot)

Here's the nexus 4

www.google.com/nexus/4/

An iPhone made out of cardbox.
Seriously.
You can't get a good service for less than $80.