Today's big $20 lens is a Sigma 75-250mm f/4.0-5.0 one-touch zoom. While the era of using one ring for focus and zoom appears to be gone forever, some fine glass was made back then that will never reappear. Compared to the JCPenney 80-200mm f/3.5 this one is both variable-aperture and inherently slower, which make it quite a bit lighter & with smaller filter size. It does add 50mm at the high end which is nice, and it uses a native PK mount not M42 - but neither lens has electronic data connectors to control aperture settings from the camera. Testing on a bright wall suggests this is f/4 from 75 to about 150mm, f/4.5 to well past 200mm before hitting f/5 at the top end. That's quite good by modern standards!
Test images show fine sharpness, very little color fringing but some 'glow' on bright objects; I should test some more with Pentax' Muted custom setting, to see if that can be better understood. The lack of fringing is a definite improvement over the JCPenney lens, and the reduced weight is nice too. I'd say that neither beats the vastly more expensive (almost $30!) 100-300mm Quantaray, which is slower but smaller, has AF and contacts to provide auto-aperture and focal-length data to the camera. All three are built for film with aperture rings. The Q-ray is in storage for a while as we relocate, so it will be interesting to play with these older lenses to determine if any of the old glass should stay with me.