There are a number of free or low cost navigation/cruise planning programs for use on your PC. I use SeaClear but have tried several others including Raymarine's Ray Tech Navigator. US charts are easy. You can download them free from NOAA. My question is" where can I get free or moderately priced raster chart (BSB) downloads for the Gulf of Mexico, the Bahamas, Cuba and the Caribbean?
Longer answer is that there may be some pirated/illegal copies available for download if you search around enough. It is, of course, between you and your conscience as to whether you want to try to take this route.