Cheap hotels / B&Bs in Cardiff

[BadHair]

Can anyone recommend a cheapy hotel or B&B in Cardiff, either near the Millenium Stadium or in town? Dp and I are going to see U2 in June and need somewhere to flop - doesn't need to be amazing as we'll only be sleeping there.
Tried the £10 Travelodge thread but funnily enough there's no room at the inn that night.

The Big Sleep hotel is supposed to be good (trendy/minimilist) & starts at £45 per night - it's in town so walking distance of stadium & shops (stadium is, conveniently, in town!). There are loads of B&Bs on Cathedral Road which is also walking distance - not sure what any of them are like but think dh sometimes puts visitors in The Cathedral Hotel.

This site might be useful.

The big sleep is one of the cheaper places in Cardiff centre to go.