Opteka 12mm f/2.8 at a glance:

• Canon EF-M-Mount Lens/APS-C Format
• 19.2mm (35mm Equivalent)
• Aperture Range: f/2.8 to f/22
• HD Anti-Reflection Coating
• Manual Focus Operation
• 9-Blade Diaphragm

If you want to go for really inexpensive lenses, then Chinese manufacturers usually are the way to go. Opteka, a US based company, released an inexpensive 12mm f/2.8 lens for the EOS M system, it’s $199.99 (B&H Photo | Amazon).

There are more inexpensive Opteka lenses in case you’re interested, for instance a 35mm f/1.7 lens starting at $89.99. Amazon too lists a set of Opteka lenses.