Diagonal lines moving from bottom to top (by 2 users)

I've had a good picture for 3 years and suddenly when I turn on the tv for the first time in the morning, there will be diagonal lines moving from bottom to top in varying width (from 1/8 " to 1/2"). The picture is not distorted while this is going on. The first few days, it cleared up after about 15 minutes. Today, it took almost 25 minutes to clear up. And right now, after being on for several hours, the lines are constant. Will this be expensive to fix.