visa extension for ukrainian

Good evening!

My name is Elena Sosedenko and i’m writing you about entry permit extension conditions for foreigners.

We are group of people of different nationalities who is traveling to Beijing in December.
Everyone has M type for business 60 days 2 entrance. Such as everyone of our group applies for entry permit in own country, some people received 30 days and not 60, but they need to stay more than 30 days and they will not have time to leave the china even for one day cause we all will work on one important project.

Could you please tell me if it is possibile to extend visa with your agency when we arrive in Beijing ?
How long it takes ?
How much your service costs ?
How much this extension will cost - police fees ?
Which documents do we need to present ?
for how many days the visa could be extended ?

Thank you for you help and information!
Really grateful to receive prompt response from you !

Elena