sometimes marriages were performed with no need for money. The Freedmen's Bureau did a lot of them as did missionaries.

Some interesting details here:
http://www.archives.gov/publications/prologue/2005/spring/freedman-marriage-recs.html

When freedom came, tens of thousands of former slave men and women—some seeking to marry for the first time and others attempting to solemnize long-standing relationships—sought help from Union Army clergy, provost marshals, northern missionaries, and the Freedmen's Bureau.