I've so far used a spare bathtub, and recycled an old coop into a brooder. If you can build a brooder and build it well, that's something you can use again and again. Here's a link to my recycled coop brooder: https://www.backyardchickens.com/articles/short-on-time-recycle-a-prefab-brooder.73985/
Other non-plastic-tub options would be things like large cardboard boxes (like appliance boxes or produce boxes from a grocer), kiddie pools surrounded with wire mesh, a dog crate or exercise pen (with openings around the lower half blocked by cardboard or wire mesh).
As far as sizing of the brooder, I'd say aim for roughly 1 sq ft per chick for first 4 weeks, then 2 sq ft to 8 weeks (assuming they're still in the brooder at that time). If you can give them a little more space than that, they'll definitely use it.
