you will also need some sort of inverter or power supply designed for auto-shutdown/startup of car pc, a new headunit and associated adapter(s)..
you should be aiming for low power usage (my PC uses under 60 watts) - just bunging a pc in the boot and connecting it to some cheapo inverter is a half-arsed job - spend more and do it properly.. achieving a stable power supply (that can survive engine crank) to the screen and the PC is important for a proper install.
other costs may include wiring/usb hubs/bluetooth/network cards/tv and radio integration/steering wheel control interface etc
no idea what wireless sound transfer is meant to mean..
I wouldnt try and do it for less than 500 quid (even buying some 2nd hand stuff)