How much will it cost to change an english registered car to spanish?

hi i am thinking of buying this chevrolet astro van which is a people carrier,i live in spain but the van is on english plates how much does it cost to change them to spanish plates,it is lhd so the headlights will not have to be altered.ist it a long process and can i still drive it round while im waiting for the plate change and correct paperwork or would i have to take it off the road.How much will it cost to change an english registered car to spanish?if you`re here in spain right now,on monday,you go to the Jefatura de Trafico of the province or place where you live here in spain and they`ll be glad to help you with this or if you understand spanish then go to the official website dgt.es in the section of Matriculacion