Help! Suggestions on how to step up my fitness regime

Hi everyone. I've been seriously committed to a fit and healthy lifestyle since last October. Since that time I've lost 39 lbs and have 24 more lbs to lose to hit my goal weight of 135 lbs (I'm 5'6"). I am still eating the same (between 1300-1500 calories) and working out 6 days a week but the weight loss is slowing down. I haven't lost anything in a few weeks. I keep telling myself it's because I'm building muscle but I'm just not sure. I get in 60 minutes of cardio a day (either spinning, running, walking, rowing or elliptical) plus 3 days a week of strength/circuit training through a gym class or Jillian Michaels 30DS.

I'm coming to the conclusion that I must do more and step up my strength training intensity to start the scale moving down again. I've heard good things about Jillian Michaels Body Revolution as well as Insanity but I'm not sure I'm willing to pay $100-150 for these DVDs. Does anyone have any suggestions on cheaper DVDs or online programs that worked for you? Thanks for the help!