What are the dimensions? EDIT: Is it the whole property? Is it underground? Are you supplying the tools? Are you letting them keep the dirt?
Sounds big, so I would say bare minimum 700-1000 r. Sorry if that seems wrong to you, I just know I did a project similar (Dug a 30x30x32 hole, which is only a 3600 block difference) and it was very tedious and took quite some time. Or is there more than one person?
see i like that number, people were asking for like 5000 i was like hahahaha ur funny. and i wish its hard to find good help somedays
But see, that is personal opinion. Other members may put a higher or lower value on that sort of job.