We charge £20 per wheel labour, spokes can be anything from 30p per spoke for Halo Plain Gauge (black or stainless) to 75p a spoke for Halo Double Butted (silver only) built with brass nipples or £15 extra for alloy (not that I’d recommend them), DT or ACi spokes start at £1.50 each.
Used hubs are fine but I would suggest new rims unless you can guarantee what usage the used ones have had.