a) All chart plotters require some chart source. Chips have become popular and are almost always proprietary to the plotter brand. Navonics chips and Garmin
Blue Chart can be purchased for various fees
depending on the coverage. Theyt are not dirt cheap
but far cheaper than all the full scale paper maps. YOu might choose to use chart books
as paper backup.
b) Downloadable NOAA charts are free. The US is now one of the few countrieds that have free charts for download. You may be able to find the old outdated CMAp charts. These were replaced with the Navonics chips when they found even a child could copy the CMap product. Other electronic charts can be found from What used to be Maptech
that would be in the same BSB
format as the NOAA BSB
charts. Thise will work in Sea Clear.
c) None of the options are free unless you stay within US waters. The NOAA charts to extend out toward the Bahamas. BSB charts for the Bahamas can be purchased. You can buy those and use what you already have now.