They have some premade stock covers for popular shapes and sizes.
If your pool can use a stock cover, they are less expensive than a custom made cover.
There are several types of fabric available, regular mesh, dense mesh, solid and solid with a mesh drain panel.
Each type of material has a different cost.
Some pools require cut-outs or other special treatments like wall anchors.
There are several different manufacturers who make a Loop-Loc style cover. Loop-Loc is good but more expensive than most other manufacturers.
Can you post a picture of the pool?