The Gambia is nice, IME. And very small. Cheap flights on charter airlines from the UK.

So you could visit Senegal in the same trip.

Cape Verde is pretty civilised and in the same area. It has a better selection of charter flights than The Gambia, from a number of European countries, and you can fly from Prai to Banjul or Dakar.

Of course, JFK-DKR or IAD-DKR would work as starts too.