I'm not sure if you maybe just need standard recordable DVD's, rather than rewritable ones? As Rik says, standard DVDR discs are pretty cheap.
But if you really need DVD RW, I can thoroughly recommend Sony's own. I bought a box from Tesco a while back, purely for the missus to re-use. She was quickly gathering a large stack of DVDR's, but now she just needs one little box of 10 RW's. Handy!
They've worked faultlessly on a Sony 560 recorder and my PC's.