Got mine off Ebay. I think it was £40 delivered.
https://www.ebay.co.uk/itm/BMW-E85-Z4-Convertible-Folding-Roof-Heated-Seats-DTC-Buttons-6948771-029/173029341094?fits=Car+Make%3ABMW%7CModel%3AZ4&epid=760064380&hash=item28495a37a6:g:MVoAAOSwLdBaMASI
This one about £48