We are doing Balsicas to Madrid return, obtained a great rate by booking through the Renfe website and not waiting until the day and purchasing a return ticket at Balsicas station.
On the day price 58.00 euros each way, booking in advance price 19.40 euro each way
For anyone expericening issues booking a ticket through the Renfe website. http://www.renfe.com/EN/viajeros/index.html
A beginner's guide to Train travel in Spain
http://www.seat61.com/Spain-trains.htm#How_to_use_www.renfe.com
Once on the Renfe webpage, click on find all stations you will then see Balsica-Mar Menor. To check the best prices click on purchase, enter departure station and arrival station and your dates.
You then should be able to see the times of departure and arrivals with the prices.
Bookings can be made up to 60 days in advance, earlier the booking better the saving`s. The internet prices are limited.