Hi More
I have one of these - they are superb. However, the 30euro mentioned is probably just a deposit.
Mine cost 20 euro from my bank (Banco de San Fernando), and I received it within a week of ordering it. It's a little gadget which you attach to your windscreen just under your rear view mirror.
Basically each time you go through the toll your bank account is debited.
If you use it more than 30 times a month (as I do) you get a discount. It is very quick, and you can avoid the queues.
Ask at your local bank for more details - I believe they are trying very hard to push them at the moment.
The website for CDS is
www.autopistadelsol.com although I cannot find one for CB.
'Hope this helps anyway .....?