I built some by cutting the tread off an old car tire found on the side of the road, tracing my feet, chopping them out, and then using some old bike tubes to create the strap part. Wife doesn't let me wear them out of the house for some reason, but they work great for lounging in the yard.
Cost was reasonable (couple hours of puttering around the garage), but you might have to get creative for arch support. Maybe you could just glue one of those sports insoles to the inside?