Thought I would have a go at making some of these as they only seem to be available for the estate Omega.
I spent a good while searching for window blind material unsuccessfully, until I happened across some midge mesh. It seems to be the same stuff that car roller blinds are made from. Mesh fibreglass.
I bought some mesh, some flexible edging strip (6mm), hook and eye velcro strip.
First I cut the material slightly bigger than the windows. I then used a credit card to push a fold of material into the edging strip. I didn't put edging on the lower profile.
I put one face of velcro around the window frames and the other around the edging strip on the blinds. After fitting and a few days of cold and warmer weather, the velcro glue parted company with the top edge of the blinds!!
So, I bought some Evo stick contact adhesive, cut the velcro strips on the blinds in half along it's length so it didn't wrap around the edging. Stuck the thinner velcro to one side of the edging.
So far this seems to be successful, but will see after the weather gets warmer. If it works, I'll make one to cover the whole rear window instead of the roller I have there now. Also, I have trimmed the edges visible on the interior pic, since taking these snaps.
ETA. The cost.
Mesh, 2 metres £10.90 inc P and P
Rubber edging £8.15 inc PandP
Velcro £4.60 inc PandP
Glue was about £4
Thats a pair of side window blinds for the Omega saloon at £27.65