Do you have one for sale? I'm still in the market for one...
Price depends on condition of cover, strap, foam and plate.
And... the style (Japanese / UK)
Bad condition: 100€
Good condition: 300€
NOS seat: 450€
Perfect Japanese (chrome bar): 600€
(rough estimations)
The cover I bought off Ebay was without the seat base nor foam nor strap.
Cover itself was in correct condition, but had some light silver paint marks on the black sides.
I think I paid 125€, shipped.
The reproduction covers appear the right pattern on picture, but they actually differ quite a lot.
More plastic shiny, not so stretchable, not so nice at all...
I had one, but didn't quite like it.
As long as your not going for the complete original look, and you don't compare OEM with replica in real life, they are good usable covers.