If you purchase the 3g iPad you will have to pay a monthly fee for a data plan (it's non-contractual). Also most of the people that I know that have them have purchased carrying cases, screen protectors, etc. which will add to the initial cost. Whichever you choose I'm sure you'll be satisfied. They are very useful tools. James White has even been using his for preaching and debating!
[video=youtube;VVodV0WB2qg]http://www.youtube.com/watch?v=VVodV0WB2qg&feature=player_embedded[/video]