This does not sound quite right. However, I can not say that this attorney could not help. Attorneys have a different experience, with regard to their practice. Some attorneys have discoverd a process and way to maneuver a case such that they could get something accomplished.
This attorney may have, as some do, a working relationship or rapport with the court and officers of the court such that they have built a strong center of trust that where they legally apply the law and are able to get things processed quickley.
However the general experience is that in this situation, when a person departs the U.S. under normal conditions, they would have to at least sign a voluntary departure form and receive a bar to re-entery. Such a bar requires a waiver which, under normal circumstanceds takes on average 6 to 18 months. It is possible to get a judge to hear a case requesting hardship waiver, and be able to enter much sooner. But, hardship waivers on average are approved only 25% of the time.
If your husband were to somehow get an attorney escort into Mexico in a way to avoid the bar, he could legally gain entry within a few days. But that assumes a lot, and I can not corroberate whether your new attorney contact can make this happen.
I woud feel more comfortable if he were so sure, that he would take a down payment term with a balance paid upon performance. I think you are taking a big risk for your money. A down payment of say 1,000 up front and the balance on his re-enter into the states would be more fair.
I would feel more comfortable if you would do a phone consult with a repesentative of the following company: http://www.fragomen.com