ScouseMouse
I don't know anything about camping, but for my money, hostales are worth staying in, and of course will probably be more convenient for the centre of the city.
I can personally recommend
Hostal Martin /
Cervelo on Calle Atocha, and if you do a search of the message board for either place, you will get plenty of info including links to their sites.
I know people who highly recommend
Hostal Lopez and also
Hostal Chelo . I have stayed in Hostal Excelsior on Gran Via which is a good budget option.
But of course there are many many more, both cheaper and more expensive.
Have you done a search for info on particular hostals mentioned by others on this board? If you type in Madrid and Hostal, you'll probably get so much information you'll be none the wiser, but it could help you to ask another question about something more specific to help you make a choice.
Where are bon jovi playing? Do you want to stay within striking distance of there? You could use that as a starting point.
As for Guinness - I live off the stuff
Well, I tell myself that it's very good for me anyway
Jo