For the Western Med you can use as well the VisitMyHarbor Raster charts.
Coverage for some parts
of the Spanish East coast
is not premium though.
And a word about S-63 charts: Those are not that expensive if you just go for the charts you need, licensing those for 3 months (they stay in place afterwards, but without updates.)
But we know as well that S-63 coverage is not complete: parts
or the Italian part of the Adria are not well covered with detailed charts. Same for Tunisia
And as for all the providers for complete, proprietary sets the quality is varying.
When I compare the Navionics charts we have for the build-in chart plotter with the S-63 charts on OCPN I stop looking at the boat's plotter.
My question for Pcav would be, what he would like to see and which ideas to complete chart offerings for OCPN he might have. More quality and accessible charts are always very welcome.