The salaries in the minors are listed on the Minor League Baseball web page:
http://minorleaguebaseball.com/pages/?id=122
While there are some variations, the general template is:
Class AAA: $2,500-3,400 per month
Class AA: $2,200-2,400 per month
Class A-Full Season: $1,900-2,200 per month
Class A-Short Season & Rookie: $1,800-2,000 per month