I would buy charts if you need them for life and death reasons but if you are open to using older charts for interest and leisure purposes you could use the CM93 chart set. This is a world wide set taken from possible copyrighted sources and crowdsourced info. Of course we cannot direct link to potentially copyright infringing files from here but this thread on cruiser forum discussing the charts may point you in the right direction.
Not sure if they work on garmin natively but they are fine with opencpn.
Remember they are about 10 years old and come with no guarantees.
Failing that openseamaps is pretty good, though lacks bathymetry data.