The CBO has a good review of the literature on the costs of illegal immigration for state and local governments. Key grafs:
Over the past two decades, most efforts to estimate the
fiscal impact of immigration in the United States have
concluded that, in aggregate and over the long term, tax
revenues of all types generated by immigrants–both
legal and unauthorized–exceed the cost of the services
many estimates also show that the cost of providing
public services to unauthorized immigrants at the state
and local levels exceeds what that population pays in state
and local taxes.
…The amount that state and local governments spend
on services for unauthorized immigrants represents a
small percentage of the total amount spent by those
governments to provide such services to residents in
For example,… the Oklahoma Health Care Authority estimated …that,
since fiscal year 2003 (the first fiscal year considered), the
services provided to unauthorized immigrants have
accounted for less than 1 percent of the total individuals
served and cost less than 1 percent of the total dollars
spent for Medicaid services.
If you look, you can find some places where the costs are significant, in San Diego for example 9 percent of the law enforcement budget was associated with illegal immigration.