They tend to be sold at a premium, though the size of this varies (without any obvious cause beyond the price-insensitivity of conscientious objectors) between the minimal and the substantial.
However, since the introduction of our three-bin system (recycling, garden and general waste), the local recycling centre has been selling compost made on its premises-and at a really good price, too.
In terms of a slightly more sustainable peat source, some "mushroom composts"-the spent growing medium from commercial mushroom farms-contain peat. Not ideal, but at least it's recycled.