Help! What can we do?

My husband is an illegal immigrate from Mexico. He has been here for about seven years. He has never been in any type of trouble. We have been married for three years and have a son together. We have seen an immigration lawyer and he told us that he would have to leave the country for 12-16 months while I stayed in the US working on his papers. The cost is $3,500. He is our only source of income and we have established a nice life for our children (he has two step kids). We need to get him some type of papers that involve him not having to leave the country and do not cost thousands of dollars. Yes, we established a good life, but we are like most
families in the country....struggling. If he gets deported, or leaves to Mexico to get papers, then my children and I will become homeless. Like everything else, it costs money. Money we don't have. My eldest son has disabilities that make it impossible for me to find a job. My son does get SSI, but it would not be enough to support the family if my husband gets taken away from us. So...my question is what is the best thing that we can do?