Aerobic/Pilates/Step class!!!! (Beijing)

Hi InterNationals.

A friend of mine and I are looking for a Fitness Club to join Aerobic/Pilates/Step classes, maybe once a week.

We both leave/work close to Guomao but it seems that all the clubs around are really expensive and ask for crazy annual membership feels!!!!!
Do you know any place you could recommend us? Even in some other locations... If the class starts after 7:30PM, we could easely be there on time...

And, if some of you are motivated to join us, we would be glad.

Thanks in advance! :-)
Camille.