Work / What is a good salary in Warsaw (office job)? [10]

Hi, I am a Mexican citizen, currently living in the USA. I was recently offered a position with my company in the Warsaw office, but I have no idea what would be a good salary. I am engaged to be married, so my salary must take that into consideration as well. I will be an audit manager with Ernst & Young, but I don't want to ask them for salary information just yet, I want to find out on my own so I can negotiate. Anybody has any ideas? 12,000 zl, 15,000 zl a month? What about taxes? How much would I get to keep net?

Thanks so much!