There is a halal butcher in rue de Lausanne, don't know the exact number but I saw it from the tram the other day -- it is quite close to and on the same side as Cornavin.
There are many Halal restaurants in Geneva, and Arab restaurants in Geneva usually even proclaim to be Halal. I think that there even are more Halal restaurants in Geneva than in Zurich. Most Lebanese and practically all Maghrebine restaurants as well as most Turkish ones have to be Halal. There are numerous such places just a bit down from Gare Cornavin towards the lake, including my favourite (forgot the name) in Rue Pradier or ChaponnieĢre.
Not more expensive than other meat, but for sure more expensive than in France. Not least as Halal restaurants have to get the meat from the Alsace as Halal slaughtering still is prohibited in Switzerland. Most Halal meat etc has the same stamp as the Kosher food, which means "controleĢ par le haut-rabbinat de Paris". It is small and hidden in a way but usually clearly readable. The supreme rabbi in Paris closely co-operates with the Muslim dignitaries !