This is going to sound really dumb until you look at it. But if you want a white backdrop that stays looking good a long time, go to the local big box lumber dealer (Home Depot, Lowes, Southerlands, etc.) and look at the cheap linoleum. Turn over the edge and find some that is white vinyl on the back side (some will be a sort of paper back, you don't want that). The cheap linoleum is about the price of a roll of good paper and is washable and tearproof and is usually twelve feet wide. Takes up a little more room in storage, but lasts a long, long time.
I am the King of cheap. Necessity is the mother of invention and Economy is the Father.