You can buy bird nesting material rings in garden centres. Wiggly Wigglers has got one for £18. I like Wiggly Wigglers but I'm sorry, that's just a rip-off, plain and simple. My sister Steph took one of those mesh bags you buy onions in and filled it with nesting materials - fluff out of the tumble dryer, bits of dried grass, teased lengths of sisal, feathers, ends of knitting yarn etc. then she hung it up in our garden.
It cost nothing at all, and it recycled some materials that would otherwise have gone into the landfill bin. It also encourages biodiversity in the garden, helping the native birds which eat garden pests. But even if the birds didn't do these beneficial things, Steph and I just love looking at them. We counted over 20 different species last weekend. I'm happy to help them build somewhere to raise their eggs, but I wouldn't pay nearly twenty pounds for a bunch of fluff.