Starting out It is fairly easy to do (budget minded) if you use foam core as suggested. I took several white background shots during my recent 365 project and other than sometimes I would clone to get rid of a seam this always worked well for me. The biggest thing was I could set it up and tear it down quickly considering I was doing it daily.
If I were taking more serious shots I would look into a similar setup but tape a large sheet of white paper to eliminate the need to clone the seam at times.
Being a Scarecrow Isn't For Everyone by EnvisionDigital, on Flickr
But hay, it's in my jeans
Setup like this minus the failed experiment of the black flash thing on the background. It did get rid of the seam, but left a distinct light to dark edge coming forward.