If you don't already own one, please don't buy one - I was in wal-mart today and those things cost anywhere from $5-$25 depending on how fancy you want it to look. Really? $25? For a glorified ziplock bag?
Okay, I personally vote for the ziplock, if something spills inside of it, it's contained, and you can just ditch the 3 cent bag and get another one. If liquid spills in a cosmetic bag, it's going to leak out through the zipper or the corners and you need to toss the whole bag.
Still don't want to use the ziploc, need something a little sturdier - look around, many items you normally buy come with a sort of baggie - for instance, if you purchase clinique, about twice a year you get a free bag with it; chances are at least 2 of the men in your family have received one too many shaving kits in their lifetimes and never threw away the bag - use it, they are VERY sturdy; pencil holders are made of nylon or burlap, these are very sturdy also and may have more than one compartment; go to the dollar tree and get one, but my Lord, don't pay $25 for one!
What can you do with the saved $25:
1 - milk, eggs, flour, sugar, butter, coffee, half n half, cereal
2 - underwear
3 - socks for 3 people
4 - a movie
5 - a new book
6 - new makeup for your bag
7 - gas for the car
8 - a christmas present
9 - groceries for someone in need
10 - enough packs of seed to plant a full garden in the spring
See, that $25 can be used so much better than on a cosmetic bag