First of all, you should understand that chemical drain cleaners seldom work. Moreover, the create a hazard for plumbers and anyone coming in contact with overflow. Secondly, in a condo you have special restrictions beyond single unit homeowners. What is needed is a professional plumber to auger the entire drain. Yes, there are cameras that can inspect inside the pipe. Costs for any plumbing services varies greatly from place to place, so it is impossible to even guess how much it may cost, but frankly, you don't really have much choice.