Basic landscape gardening job - price?

[monthefish]

I have an area of garden on a property, 15m x 40m, currently covered with reasonable quality topsoil (but will need the larger stones filtered) that is to be grassed.
Area has been levelled by means of big JCB, but will still need to be levelled further to get it nice and even for the sowing of the grass seed.

I had a landscape gardener look at the job (to prepare and seed the area) last night and will get a quote from him in the next few days.

Any suggestions on how much it might cost?