Funny but that would probably work.
Actually you might be able to craft some sort of boxed frame on top of the dog house that the lap top could sit in. Certainly would keep lateral moment safe, just need to worry about severe bounce depending on how deep the frame is. Just a thought.
I have the iQue from Garmin. Find that with voice commands I can keep having to look at it down. On the trail, again mainly for reference at times.
I think I have seen someone selling a metal mount that attaches to the windshield pillar as well. This might be the $500 solution your talking about though. Not sure on cost.
Oops found it...
http://www.bluehummer.com/radiotray.html actually for radios but perhaps they could fabricate one for a laptop. $140
2001 H1 Opentop
Former 03 H2 Adventure Series
Homepage:
http://www.hummerh1.net