In reply to diablo:
2 different things.
Why not get both ?
Pull up bars are £8 in argos.
Fingerboards can be used for pull up training, lock offs and one arm work. However if space is an issue you can buy a small board and a removable bar as well. Use the bar for pull-ups - not that productive for training - frenchies, lock offs, typewriters etc.
My fingerboard is a metolius rail - but i don't think they make them anymore. Very basic and was only £20.
Lots of people buy a strip of wood about as deep as your first finger joint and screw it above a door.Search on here for making your own.
Rock rings ( again from metolius ) can be hung off a bar and the whole thing then packs away when you've finished.