You can buy a pre-paid cell phone from $80 more or less (a cheap one). They come with an initial charge of $20 aprox. However, you could find special offers. I'll look for them in FNAC (plaza Callao), Alcampo, Carrefour and big department stores. In Spain, there are 3 companies: Vodafone (ex-Airtel), Movistar and Amena. Amena is the cheapest one but it gives you less services than the other two. Movistar is the mobile branch of Telefónica (it has more coverage and it's the most popular, followed close by Vodafone). I have a Vodafone, it works well but the customer service is awful (even by Spanish standards!)