AFAIA its 30,000 @ 24% @ rate of tax+PRSI at 6% or 2%
If you are on the lower rate of tax the BIK could push you into the higher rate or if you are paying the full rate of PRSI BIK or part of it could be reduced to 2%
Assuming you are on the high rate of tax and paying less than 46600 pa including BIK or where 46600 is not exceeded in a pay period (cumulative) i estimate the BIK to be 288 pm
There is a slight alternative you can take up with a few conditions to be met. Basically because you spend more tan 70% of your time away from the office your taxable value can alternatively be calculated at 35K * .3 * .8 which gives the same result as asdfg.
This would be more advantageous for example if your business mileage was 14,000 PA.