This spring was my first foray into chicks. I bought an extra large dog crate, and lined it with cardboard, as the bars are far enough apart for the baby chicks to fit through. If I need to have a brooder again, there it is. Six chicks lived in it until they were about 5-6 weeks old, no problem.
Yes, it was $85. But I have other uses for a large dog crate besides as a brooder, or even for a dog, so it was a good investment. One use that I have every year is to harden off seedlings for the garden. They're safe from rabbits or birds, and I can throw a sheet over it to diffuse the sun, or a blanket to hold in warmth at night.