The 7Artisans 35mm F/2 is currently the lowest cost M-Mount lens on the market.
Made in China by 7Artisans, the 35mm f/2 lens is Leica rangefinder coupled M-mount lens. With modern coatings, it is high in contrast and has stacks of character.
You can read my review of the prototype version here
I am one of the only UK dealers of 7Artisans lenses and have a good relationship with the team in China, so if you do have any issues it is me you deal with in the UK, and I deal with my contacts at the manufacturer to solve the issue quickly. This is often not the case when dealing with Chinese dealers on ebay who can be slow to reply, especially if the issue develops after a number of weeks or months.