Hi,
We are going on a an employer sponsored visa (457), the immigration website says that most of these are completed within 8 weeks although this can obviously change depending on volumes. We are lucky enough that my partners employers have an agent that they use and everything is being done for us, they have told us that it should be 8-10 weeks. We aren't paying for it but the cost was only about $500. If you are looking at a skilled permanent visa I think it is more like a year and $5000. I could be wrong on that and I'm sure someone will post the correct information if I am. You could also look at
Department of Immigration and Citizenship there are information booklets on the various visa and you can follow the links to find out the costs and timescales involved.