Let's go Fitness are among the cheapest, and you can even have reductions depending on your insurance (200.- off the yearly price with Assura).
But it's still about 80.-/month. I don't think you can find cheaper here...
Or take good value fr your money, and go the Malley fitness centre! For about 120.-/month you also have access to the pool, jacuzzi, sauna, hamman... I love it there it's great!
Oh, and stop comparing with 'back home', wherever that is... You'll end up in a nervous breakdown soon otherwise!