Amazon has really cheap bannetons with free shipping today in case anyone is in need.
Amazon are still charging about £10 per banneton. The ave price for one seems to be £10-£14.
However, given that all a banneton is, is a basket to provide support to dough and impart a pretty pattern you can use almost anything. Any bowl with a teatowl inside for example.
Nevertheless, check out this website which sells wicker baskets of all shapes and sizes from 0.50p upwards. Absolute bargains.
Remember, if you think the bamboo or wicker isn't suitable for food then just put a liner inside that is.