20,000 Kms per annum at civil service rates amounts to 6,437 x 59.07c + 13,563 x 28.46c = €7,662.
Expenses
Motor tax 500
Insurance 300
Fuel (30 mpg) 20,000kms @ 11 km per litre x 1.36 per litre = €2,472
Service 1500
Depreciation €2,500
It could be argued that you have to tax and insure the car, it will depreciate either way and will have to be serviced so probably works out about even.