Price depends on the condition therefore the amount of time to strip and restore the springs and padding etc.
The main element that contributes to cost is the fabric, how much you need (a deep button back sofa like the one show will use more fabric) and the cost of fabric per metre.
When we strip a sofa or chair we are able to see all the joints and clips etc that hold the frame together and attach the springs and in some cases mechanisms. So, often we can’t tell exactly how much work is involved. Therefore we assume some internal repairs are required and factor this in to the cost to reupholster your furniture.