iPad 2 3G plan cost (att & Verizon)
Macworld has a chart with a lot of that info here http://www.macworld.com/article/158361/2011/03/compare_ipad_data_plans.html

They also note (for your pre/post paid question):


  That means that you can sign up for a month, cancel the plan afterwards, and then sign up for a separate month at some point in the future. However, while AT&amp;T now offers both prepaid and postpaid options for data plans, Verizon only allows you to pay for data upfront. 


As far as termination fee, neither are charging activation it looks like either (in the US). So you don't have to terminate it like a normal phone/data plan, you just pay for it the months you use it.