i've recently used a solicitor to do mine, all in cost 140 euros, took 6 business days to get the new log book!!!! thought that was good as my last car cost 180 euros to transfer and it was only a 1.4 fiesta plus i had to pay for translator (40 euros). this time i knew more spanish and the car was a 1.8 mondeo, and as far as i'm aware the price increases with the engine size.
worth a try if and if you want i can make the phone calls to arrange it.
here's the solicitors details~ Gestoria Fdez Breis SL, Apartado de correos 29, calle Moreras 28 Bajo D, tel/ 968 800 733.
the company is based in Alcantarilla, about 10 mins from nueva condomina shopping centre.