Did some shopping uptown and got very, very lucky finding pre-owned stuff:
From Game:
Rock Band Portable Drum Kit: £12.99
(THIS! was exactly what I needed. I mostly wanted that portable pedal to replace the Guitar Hero one. Even better, is that it has no loose parts, a nice curly stretch cable, (but is long enough not to reall need it), and I can use them with Rockband if I need to!

)
Rock Band: The Beatles £4.99
(I'm not really a fan of The Beatles, but its more songs for a cheap price!

)
Band Hero £4.99
(My buddy has all the other Guitar Hero games, plus Its actually got a decent setlist. Its all pop, but its not all crappy like GH5's, great game for the microphone)
From CEX:
Rock Band £4.50
(More songs! Plus I have the drums now)
Rock Band 3: £15
(OMG! This was a great find! This game is pretty hard to get a hold of, (there was only 1 copy in store), especially for that price! Got some great songs, plus, Rock Band eclipse Guitar Hero in DLC, so I've already got some DLC for it!

)
So overall spend on Guitar Hero/Rock Band stuff:
Guitar Hero: Warriors of Rock Band Pack £42
Rock Band Portable Drums Kit £13
Rock Band £4.50
Rock Band: The Beatles £5
Band Hero £5
Rock Band DLC: £10
Thing Called Love
Brutal Legend Pack
Transmaniacon MC
Stand Up and Shout
Child in Time
Gutar Hero DLC: £7
Black Betty (Cover)
Rocky Horror Pack (Sweet Transvestite, Hot Patootie, Time Warp)
Detroit Rock City
Tom Sawyer
(NOTE: I got the Guitar Hero DLC first)
OVERALL SPEND ON GH/RB STUFF: £86.50
Man! Thats a lot!
(Well not a huge amount considering 2 brand new games would cost around £60-70, and I have most of the instruments, but its still quite hefty. Great value though, would last me quite a long time. Especially if my buddy comes over, (as he has Guitar Hero: Metallica, Van Halen, 2, 3 and Greatest Hits on 360, (he might have 4 and 5 but I can't remember)))