There are other companies out there, Ya.com, Wanadoo which you might be able to get a better price. Keep in mind though that in Spain, Telefonica is the traditional government backed company and I am pretty sure they own most of the lines. I think that is why most of the companies have the same price for their DSL.
One final note you can find a few prices a little bit lower but they actually limit the service so you don't have 24hour access. So you can use it at night or offpeak times...I have never seen that before in the US, those were around 30Euro/month...to me the extra 10Euro was worth being able to be online all day. I hope this helps and if there ever is a website that would be awesome...it was such a pain to try and read Spanish and then call people and try and ask questions...so painful.