I deliberately did not choose a 3G version because I don't really need a monthly data plan which with my currant provider, AT&T would cost me $360 per year. Also I have WiFi at my house and free WiFi is available at the airport.
I plan to adapt the iPad to my existing PC mount that I have on my yoke.
You are not required to get a data plan with the 3G version. The 3G version gives you a built-in GPS, in addition to the 3G capability. They usually cost about $139 more than the WiFi only model, so not much more than buying an external GPS and you then have the option to turn on data in case you need it in a pinch.
The built-in GPS has worked very well for me.
I got my 3G iPad strictly for the GPS. However I made the mistake of trying out the data plan one month and could not turn it off afterwards. It is just too convenient for me. Where I live, and for traveling internationally, I find AT&T better because they use thee GSM system. I also have my phone with AT&T because I can use date and phone simultaneously. Coverage where I live is just as good as Verizon.
You'll have time to decide how much data you'll need. You can easily change plans from one month to the next.
Merry Christmas, Amy!