I used to use Fugawi Marine ENC a lot - but they also have a cheaper version for about $135. You can use just about any format.

http://www.fugawi.com/web/products/fugawi_global_navigator.htm

IMO fugawi rocks - the best out there for the money. We would scan charts and use Canvas with the GIS pack to georeference them, save as a GeoJpeg, and use it with fugawi for navigation.

You know you're in for a rough night at sea when the barometer does this: