You can either buy these at the store for around $30 or make it yourself for about an hour of time and around $4 (less if you have coupons or buy the tulle on sale).
I have made one that is just white and another with three colors; pink, white and brown. The pink is harder to see and I would suggest either doing two pieces at the same time or trying to find a darker pink so it shows up more.
The possibilities are endless for color combinations, size and fluffiness.
Here is all you need; Elastic, whichever size you want of which I used leftover I had from making me and my husband's pajama pants, and a package of 25 yds of 6" tulle that you can get at almost any craft/hobby store. Both pictured below.
It's easiest to cut all the strips first so that you can loop them onto the elastic all at once without having to stop to cut more strips.
The length of the strips depends on how long you want the tutu. Just measure how far you want it to go on your little one and then double it and cut. I used all of the 25 yards for the white tutu and about 35 yards for the multiple colored one. Just depends on how fluffy you want it and how long you cut the strips.
Measure the waist of your little one for the length you need the elastic and then either hand sew it or use a machine then put it on your leg to attach the tulle.
The video below shows how you loop a piece around the elastic.
Good luck and have fun making your own!
And here is the white one on my little Sweet Pea.