Front vs. Rear and Ground vs. Truss vs. Rigged
Front vs. rear has no cost difference. Rear projection requires space behind the screen to focus the projector which will impact the venues seating capacity. The front is generally brighter projection but means people may have to walk thru the projection to get to the stage if the traffic flow cannot be controlled.
Front projection can be done from an AV cart in front of the screen or, if the ceiling is high enough, from trusses at the back of the room, projecting over the seated audience. Front projection can also be done from a suspended (rigged) truss that is attached to the ceiling. Rigging is the most expensive form of projection. Sound systems may also be rigged.