paying $150 to do jumping jacks for 40 mins in front of a tv is pretty lame in my opinion... (that's pretty much what insanity is)
instead like someone suggested earlier, I would get a stopwatch and some running shoes, pick a 2-3 mile path and go for a jog or (walk+jog intervals) around the neighborhood, each day run the same path and no matter what happens resolve to beat your previous day's time even if only by a second... nothing motivates better than seeing results (time going down) right away...
if anything, get p90x at least you will get some variety and will learn some workout techniques... insanity on the other hand is 15 very similar workouts (which all are pretty much 40 mins of jumping jacks)...
(I'm pretty sure they even recycle the footage between the dvds..
)