The dealer can arrange the transfer for you, very simply, just by filling out the relevant DVLA Transfer of a Cherished Plate form. There is a transfer fee which used to be £80 but it may have gone up by now (it's been many years since I last did one), but the dealer shouldn't charge you anything on top of this. It is, after all, just a case of sending the completed form and payment to DVLA at the cost of a postage stamp! All the details you need can be found here...http://www.direct.gov.uk/en/Motoring/P
ersonalisedRegAndNumberPlates/DG_4022576