I have built up the amount of equipment I've had over the years so I have dumbbells, kettlebells, etc. I did buy a nice set of bands though for the pullups though because at just over 200 lbs, I am not doing pullups, assisted or not.
So you may need to make some equipment investments but I think it is well worth it. I love P90x so much! Really, it is an awesome program.
One thing I have decided against in the recent past though is that I don't want to buy adjustable dumbbells although I know many people have and like them. I have a set of dumbbells up to 20 lbs and beyond that, I have kettlebells. My only issue is that I can't find an inbetween size of kettlebells from 25 to 35 lbs. I think kettlebells are more versatile than dumbbells so that is my own personal choice.
Bands though are very versatile and you can travel with them and get a good workout on the road. The TSA didn't look too kindly to me when I tried to take a kettlebell on the plane so resistance bands are really the way to go
Oh and I know Beachbody recommends building up to P90x by going to Power 90, maybe Chalene extreme and then P90x. I chose for myself to just buy P90x because I figure I could modify the workouts and I have. I've shown vast improvement in strength and abilities in just a few weeks. I am amazed really.