I just put one together my self for around 70$.
I got a free laptop it is an OLD 133 omnibook 800ct it only has 16 MB of ram and 1 gig of H/D space. I was able to load an old version of Nobeltc and all the Maptech digitial charts for the puget sound on the Gig of space. I wont go into were the software came from.

I went to walmart bought a 300 watt inverter that plugs into your lighter for 40$. (you can take this in the car or what ever)
Then I bought me a Alumimun suitcase and outfitted it all into the suitcase so if there is any water near by I just close the lid and walla instant water proof 30$ for the case.


Elk run.
As far as software goes I would use OziExplorer . With that engine you can scan ANY chart and it will calibrate it for you . If it is a big chart you can take it down to kinkos ans the can scan it for you.