Traveling in the US - Internet, GPS, mobile broadband access?

I will be going to the US for three weeks this summer, traveling coast to coast together with a bunch of Swedish students. My plan is to make our road trip a “real-time event” on the Interwebs as well, using GPS, video blogging etc. We will stay at hotels and campsites mostly. So I have a couple of questions for you US peeps.

1) I will probably need a US sim card for my phone. Preferably an operator that also has unlimited Internet surf. I won’t sign up for a contract or anything, it needs to be a pay-as-you-go or prepaid sim card. How much would this be and what operator would you recommend?

2) Are there any operators offering prepaid/pas-as-you-go mobile broadband?

3) What is the Internet situation like on campsites generally? I heard someone said that quite few US campsites offers free or cheap wifi.

Would be great with some feedback and ideas!

Cheers