cheapest would be nes_shades, even cheaper would be red perspex, but perspex is not as safe as shades designed for safety, if in doubt give it a blast with your laser to see if any light gets through.
The WL lasershades are not as dark as the nes shades. But either one will provide adequate protection. I too have the WL shades for both green and red protection, and love them.
I won green laser shades and sports goggles and red laser shades from WL and they're good products. I just don't really condone buying from WL. Nes shard would be a great option but those lasershades are nice. But $18.99 shipping.... Have you looked at the goggles that Nova sells?