Two "group" recommendations.
All from very cheap to cheap.
1) early "auto" Tomioka-made f/2 chrome nose fifties. Usual 6 elements Planar based design, but a not-so-usual build quality, typical of the best lenses manufactured at the peak of Japanese industry mechanical quality.
I never considered "slow" normal lenses, cause I love super fast manual focus optics, often shot wide open, at night or with scarce illumination. Though recently I've found that at f/2 I can still get a creamy bokeh and enough separation between focus planes.
Recently I bought a Mamiya/Sekor Auto 2/50mm and a Yashinon DX Auto 2/50mm.
I wanted to find out if they came from the same maker. At first I had some doubts, cause they are actually different, but later I found a picture online that shows a Yashica lens identical to my Mamiya. So yes, all of them are Tomioka's.
These lenses are small enough, and a real pleasure to handle. Once I re-greased the helicoid of the Yashinon, both operate as new. Very much Super Takumar-like
If you want a single coated fifty to control contrast, or to shoot portraits on APS-C, this family of lenses is definitely worth considering.
I suggest chrome-nose or half chrome examples, cause I believe that if you choose to go vintage and single coated, better go for early versions.
Second "family": late silver PENTAX-FA lenses made around the turn of the century.
I have three of them: 4-5.6/35-80mm, 3.2-4.5/28-105mm, 4.7-5.8/100-300mm.
The first and the third are respectively dirty cheap and cheap. The 28-105mm is a little more expensive, but still very affordable.
Paid mine 130 US dollars shipment included, in spotless condition and with original caps and shade. Without shade and sold with an MZ body the price could be a little less. Not so much though, cause it's a cheap alternative to the new D FA version. The price is also affected by the build quality. It has metal bayonet and feels more solid than the other two.
Build quality is the weak spot of these lenses. I opened the 100-300mm to try to clean what I thought was a tiny fungus spot (but found a principle of flower-like separation): unlike previous partly plastic zooms, cheap plastic is used for parts that had always been made in metal. Not just plastic threads, also optic groups encased in unopenable plastic casing. The 35-80mm, albeit looking new, is especially wobbly.
On the other hand, these lenses have good AF on recent bodies, including the K-1, and provide enough sharpness stopped down (especially away from the extreme end of the zoom range).
The price/performance ratio is very good. Beyond resolution (that is quite good stopped down and decent wide open), the forte of this family of lenses is the brilliance of the pictures. High contrast, beautiful colors, and good flare resistance. This kind of performance really surprised me. The pictures don't need PP if correctly exposed. Considering the price, it's quite impressive.
It seems that this generation of lenses shared common design goals. Considering the reviews, I suppose that these three objectives do better than other members of the "silver FA" family, but I can't confirm cause I have only 3 of them.
Two considerations.
I'd buy only examples in very good shape.
I recommend these optics to all the K-1 owners who prefer to invest their money on expensive high performance primes. It makes sense to own a couple of cheap AF zooms when the situation doesn't allow for a more reflexive, slow paced shooting style, or we are afraid to damage our expensive objectives.