Lots of mistaken info here, I've just been through this process so covered the ground;
*It doesn't have to a commercial before you take it in, as they're not manufactured in the plant as commercials, this is an Irish practice, they are converted for Irish tax reasons. Ever see the same number car-derived vans in UK---No.
*If you convert it yourself, then it has to be inspected by Revenue to ensure its a bona-fida commercial.
*The VRT is not flat rate €50 on car-derived vans, See the revenue VRT website. Only manufactured vans are €50 flat rate (ducato, hiace, primastar etc) So VRT is going to be more expensive than you are expecting.
*VAT is not applicable if the vehicle is over 6 months old OR over 6,000KMS, not 'and' or miles. See revenue website
Work the figures again.