I've started doing some research about current carriers in the US to find something comparable to AT&T's current iPad data plans. There are a ton of smaller less known carriers and virtual carriers that can even use the same networks as ATT/T-Mobile but give much better prices for talk/text(List of United States wireless communications service providers - Wikipedia, the free encyclopedia. However data plans on these lesser known carriers either is non existent or unbelievably high priced.
There is one called Consumer Cellular and here are there crazy data prices.
Monthly Limit | overage | Monthly Price
2MB | 1¢ per Kb | $5
15MB | 1¢ per Kb | $10
30MB | 1¢ per Kb | $20
Offers $34 unlimited wireless data aircard (would have to call and find out if they can add the plan to a simcard).