You are wise to plan ahead—and at least be able to offer the best information available to your husband and his family when the time comes.
All states--and many
counties and municipalities--run programs that offer financial benefits for funerals, burials, and cremation to families that have limited funds. Unfortunately, there is no good central resource that tracks all of them--and what is available varies widely, depending on where you live.
If your father-in-law is receiving some type of public assistance, the family should first contact that agency. Otherwise, the best way to find out about the specific benefits offered in a particular locale is to do an Internet search of the state plus the county plus the words "burial assistance." It is often the counties that have the most targeted funds available.
To secure any of the benefits, survivors have to fill out an application that the state or county agency will provide, usually including a brief listing of available cash, property, and other resources. So it would also be wise for you to start collecting this type of information now.
Another place you might turn for good guidance is the Funeral Consumers Alliance--a nonprofit group aimed at helping consumers keep funeral costs affordable.