Consider the early Vivitar Series 1 35-85 f2.8 varifocal. This was made in M42. They're not common, but show up on eBay from time to time. They are a bit flarey (they have about a zillion lens elements) but are sharp as hell across the whole focal length range. Build quality of the early Series 1 was on par with the Asahi Takumars, i.e. luxury quality by today's standards.