SLR Magic m4/3 HyperPrime 12mm f1.6 lens
This is probably one of the fastest in its price range of wide-angle lenses you can get. It’s a 12mm (equals 24mm on full frame sensor) Micro Four Thirds lens at f1.6 and costs around 550 USD + vat. Although this 12mm is still a speciality lens I have been using it quite a lot already.