I think is a great idea.
Provided the 'acceptance' of the job was automatic, meaning anyone could 'hand-in' what was required and receive the reward. Otherwise, if the 'poster' could control when to accept the hand-ins, Gil farmers could use it as a legitimate way to transfer Gil to other players.

I believe this system would work great if made available in high volume only to those that own housing(anticipating the lower costs). This would give a reason for others to come to your Free Company(or personal when it comes out) housing. As well as allow you to not allow non Free Company members to your housing, thus making an in company economy. Free Companies known for being merchants would leave their house open. Less social Free Companies would use it to benefit their members with reasonable prices, so everyone is 'up'.
A looking for work main board at the housing district entrance would be great, with an individual board for each house.
Then a standard Work Board in the capitals, which would allow 1 post per player. With the Free Company Work Board allowing many more posts.