Cost of installation for antenna

Yes, it will track while underway. That's why it costs so much. However, you will lose the signal if tress, poles, bridges, tunnels block the line to the satellite. If that's what you want, go for it. Just most users find the novelty wears off really, really quickly.

I was led to believe this unit will track while under way. If not this unit, which unit will track?

Install a Trav'ler and a DVR. Record shows good for the Grandkids and let them watch that when you choose and have them enjoy the scenery when you are in those areas (the Interstates are mostly boring!).
The Trav'ler does not work will in motion, but a DVR works great and you get to watch programming you (and the Grandkids) like when you want to watch it and not only when it's being broadcast.
The Trav'ler is full automatic. Once parked you push one button and 5-8 minutes later you are watching (and recording) full HD from either DISH or DirecTV.

Yes, the Trav'ler is a good unit, but it requires setup/search when deploying, yes?

I'm considering grandchildren while under way. Of course I would prefer they see the scenery, but there is the cel phone addiction problem.

Very few folks with in-motion antennas use them as much as they thought they would. Many end up not using them in motion at all at a year or so goes by. However, if you want to pay all that extra money you can plan on about $1400 for the antenna and $400 for installation from a private satellite TV installer. You can watch Camping World (if you don't mind Camping World) for installation specials as they will often do an install for less than $100 (as low as $39 or $49) if you can catch one of them.
For about the same money you could have a Trav'ler! (Yes, it will fit).