It's not cheap and this is cost...
Display: $140
Arduino Mega: 15$
Display case: $15
Main unit case: $15
Oil and fuel pressure sensors: $25 each (x2)
Oil Pressure Adapter Plate: $30
Fuel pressure adapter: $14
Coolant Sensor Adapter: $20
Stainless NPT adapter: $5 each (x2)
Temp Sensors: $6.00 each (x2)
Thermocouple EGT sensors: $15 each (x4)
Thermocouple Amplifier, 4ch: $50
Stainless bung for EGT: $5 each (x4)
Various cables and wires: $30
Various connectors and misc parts: $50
Power amp relays: $10 (Optional)
Audio switcher: $60 (Optional)
Beer: $25
$556 - $626