If you are looking for a soft top, you'll probably need to save the money by fabricating your own shelf. The last soft tops I saw in any reasonable condition were being sold on eBay and Gumtree for ~£400-£500.
The Shower Covers turn up more regularly and seem to sell from anything between £50 and £100, but they do not look to be anything substantial, and are literally something to use in case of an emergency rainstorm, while being in the vehicle.
The original shelves do also turn up quite regularly on those auction sites, and tend to sell for upwards of £80 for one in decent nick. That may not however include the brackets, which I've seen go for about £50. It is straightforward to just rest the shelf, either original or fabricated, on something that sticks out of those (removable) lugs that are near the top of the rear quarter panels. You can use the lower ties near the rear door to do what the original cover does, and secure with an elasticated stretchy thing to hold the shelf down nicely and prevent bounce/vibration on the rear of the shelf, (if that makes sense?).
The original does look as if it is locking; it has a similar looking lock to the boot cubby hole. But it is just for show. The elastic is what holds the shelf down. So you are not missing out on anything there if you do make your own.
Jim