my best guess is they run along Forester Road, when it hits end of this road, will follow the transmission line to Marsden Park
Station 1: between Ropes Crossing and Tregear
Station 2: between Willmot and Shalvey
This option path is cheap. Looking at a google map, Transport for NSW only need to acquire either the commercial or residential of Forester Rd after St Marys station. The rest of this path are mostly government owned land, flood prone or rural that is dirt cheap.
On southern side of St Marys I would think a station at Colyton and St Clair would be economical feasible.
Though there are draft plan to put track though St Marys, this may change so it goes to Penrith Station instead, as it is a major hub.