Post Office box (Apartado de Correos) - cost of annual renewal?

I don't yet live in Spain but have an Apdo.de Correos.

As I have had to cancel my forthcoming visit to Spain because of illness, I shall be unable to go into the Post Office to pay my annual renewal fee before the mid-February deadline.

I should be grateful if anyone could tell me how much the fee is this year, and also how to send payment (I know they will not accept a cheque).