Debt management plans are estimated between 1.7 and 2.5 percent of your enrolled debt (the accounts accepted into the plan). If you enroll $30k in a DMP, your new monthly payment will be between $510 and $750. You need to contact an accredited DMP provider in your state to get an exact quote.
Both the National Foundation for Credit Counseling (NFCC) and the Financial Counseling Association of America (FCAA) are good starting places for finding accredited agencies, which should have counselors certified and trained in consumer credit, money and debt management, and budgeting.