For a slightly less absurd version, use the Mistuhama Tomino. Add a rigger coccoon plus armor, weapons and cyberwear to taste. Runners on a budget might use any of the Medium walkers instead. The addition of a Rigger coccoon will make them noticably larger than human size but still smaller than the Tomino. Even the Beaver could be converted to something Tachikoma like. Just depends on your definition of power armor.