Price difference between master's and phd programs
Masters students are often unfunded. That is, they have to pay (most of) the tuition fee. Against that, PhD students are typically funded. That is, they are paid to study. Here's an example. The student here is not only paid a monthly stipend of $2000/month, (s)he doesn't have to pay tuition fees.

In other words, yes, it's often cheaper to do a PhD than a Masters. Caveats apply: it's possible you may not be offered funding (in which case a PhD is also more expensive). Also, since a PhD takes longer than a Masters, if you graduate with a Masters and then get a well-paid job immediately, the extra income might be enough to compensate for the price difference.