ive got white and black muslin sheets which are fab to use, i occassionally us a huge fleece blanket thats nearly white (off a kingsize bed) which has given me some good results too- although alot harder to deal with shadowing etc...
more recently though ive been experimenting with shower curtains or various colours and getting some plesing results.... the do crease easily but if you keep them taught their great to use in my opinion, especially when i illumunate behind through a diffuser
i was looking on the internet for some cheaper stands/backdrop sets, but the majority of the 40-60 quid ones had negative reviews about the material being to thin or not the size they advertised etc... i went to asdas home shop, spent about 30 in total on 2 clothing poles, clamps, fleece blankets, and 6 different colour backings- and ive found its more manouverable than what i would have purchased so im well happy!