When we obtained our NIE in 2004 we attended the main police station (in Benidorm) with our passports, photocopies of passports and a couple of passport photographs. As we were buying off plan, we also took along a copy of the contract which showed the development address.
Our NIE’s were ready in 2 weeks and our estate agent picked them up for us as we were back in the UK, faxed us copies and returned the originals to us on our next visit.
No charge was made by the authorities at all and apart from waiting for a couple of hours in the queue, all was very smooth and uncomplicated. Hope this helps.