Another Vespa, for the cheap lens (only lenses under 100 Euros) thread in a German forum. I used a Nikkor AIS 50 E for it which goes for about 50 Euros on Ebay. I got this lens for free, it came with my Nikon F3 :). It is not a Summilux in terms of Sharpness but it does have a pretty decent rendering.
Sony A7 // Nikkor 50 AIS 1.8