Also from the perspective of engineering, if I wanted to DIY an accurate corner reflector cheap then I'd use the property of returning laser beams to their orig

Also from the perspective of engineering, if I wanted to DIY an accurate corner reflector cheap then I'd use the property of returning laser beams to their origin over distance to do it. Make a jig to hold the three mirrors, make sure they can be fixed to the jig firmly and glue them up. Test the ability to return a laser over distance. Calculate (somehow...?) the error in the jig, adjust it, rinse and repeat.