P90X is a do at home training system that costs around 130 dollars,ONE TIME Payment.
Cross Fit does offer more in regards to variations and additional intensity by use of varied weight exercises,but cross fit costs A LOT more than P90X.
Cross fit became the word for training outside of your designated sport,to keep boredom from setting in.
Eric Heiden for example Bike riding in place of speed skating training.
Now cross fit and muscle confusion has taken on a new meaning,as the way it must be done to make gains,rather than reduce boredom.
Funny the Navy SEALs are probably the most fit of the Military and they do not use or need muscle confusion,they use muscle exhaustion and adaptation to need,using the same general fitness exercises we all know ,push ups,sit ups,pull ups,running,and lifting objects like logs and rubber boats as a group.
Navy SEALS WOD tire the whole system through intense exercise and constant activity in realtion to working needs.