What model of Advent are they? Large, small, original, New Advent?
surrounds can be replaced at appox. $50 to $75 plus shipping. If you are handy and can follow the instructions exactly, you can probably purchase the surrounds for around $25. I had a pair of the New Advent Loudspeakers which I had surrounds replaced. Yes, the sound is a bit dated but they always sounded respectable to me. I gave them to a Nephew who didn't have a lot of money to spend on hifi. He was absolutely thrilled with them. Also gave him a a refurbished Sherwood 7900 receiver and a Marantz CD player. He couldn't be happier.