Calorie burn for DVDs?

What's the best way to guess what I'm burning when doing workout DVDs? I'm usually doing PINK method and Hip Hop Abs. I like to throw in Bob and Jillian in there every now and then too. :-) I can't afford a heartrate monitor at the moment...so I need another way. Like I said, best way to GUESS...I know that without the heart rate monitor I can't get an exact number..... help please?