I can't speak for the US, but here in Canada prices have gone through the roof. When the iPhone first came out you could get a 6GB plan for $55/month with Rogers. Now for 5GB you're looking at $105/month, bring your own device.
In Saskatchewan, for example, there is a public sector telco (Sasktel) that provides the same services that the big three national telcos (Rogers, Bell, Telus) provide. As a result, the prices in Saskatchewan are significantly cheaper than in neighbouring Alberta (where there are only the big three).
It's very eye-opening to go to the Rogers site and flip between AB and SK to see how the prices change.
I'm deliberately excluding the smaller players like Wind because they don't provide the same service, the smaller players lack the geographical coverage that the big three have.
I'm from Saskatchewan, and I can say that Sasktel is quite a good ISP and telco. Despite the relatively small, sparse population of SK, the prices are quite low, and I think Sasktel is the major reason for competitive pricing.
As a direct example of the Rogers pricing difference, the 10 GB "share everything" plan (unlimited talk/text) costs $65/mo in SK but over twice that, $135/mo in AB!
Are you including voice in that? I'm still on the original promo plan (gotten when I didn't even have an iPhone, since it didn't do tethering yet and my Moto RAZR2 did), and it's $30/mo for the data alone.