From Fallen London Wiki
this is 150 moonpearls for 4 echoes, on average, making each moon-pearl cost 2.66 pence; this is marginally cheaper than buying them at the bazaar, and the wounds are negligible when amortized.
so: screw being a woeseller! the real vanity is staying at 399 woesels, so that whenever one is in need of pearls beyond price, one can become a woe-seller. :3