once metal is broken... the weapon becomes weak... but once the broken weapon is sold blacksmith could try to repair it... or to forge another one with the metal of the previous one...
so the price of a broken sword will be the price of the metal nothing more
it may be interesting to create a very very good blacksmith, a unique one in Yliakum, he will be the only one to be able to repair a broken weapon... hum off course the price must be particulary impressive...