Check out the following link for cheap charts of the world... this guy is into sailing, but don't hold that against him!
http://www.michaelbriant.com/charts_of_the_world.htmI came across this last week while in the UK talking to a friend that sails. All runs on a laptop with Windoz XP (probably OK with Windoze 7 but NOT Vista), and all you need to add is the USB GPS antenna (there is a link for this device on the web site). You can do nice things like print out charts, and plan your route before you even leave home! I am planning to run this on one of those Acer EePC laptops (cost about $400), so the whole combo will give me a global, extremely powerful 10.4" color chart plotter for under $500...
Hope this helps and maybe gives you some ideas... it works for me...