Was on the ST website last night and noticed they were offering a $2.50 monthly discount if you signed up for Auto-Pay before 1/28/15, which I have had in place previously on their 3GB data $45 monthly plan. Although the discount option was not available to an existing subscriber, I found that if I unsubscribed from Auto-Pay, the option to get the discount was then available, and I could maintain the same renewal date - I was able to get the discounted rate going forward. The new rate is now $42.50 plus minimal tax, which makes the rate, especially for the AT&T network, the most competitive I'm aware of for a 3GB or similar data unlimited plan.
https://www.straighttalk.com/secure/autorefill
https://www.straighttalk.com/secure/autorefill