I have a Macht Schnell Clubsport Seat Mount for sale. I used it for a few months for a Recaro Pole Position on my F80 M3 but according to Macht Schnell, the seat mount will fit a wide range of BMW cars including E9x cars. It is a decent all-in-one solution that will fit most bucket seats and offers a low seating position and manual seat rails.
I'm selling because I daily the car now and switch back to stock seat for comfort.
The set originally retails for $295 and I'm asking $175 OBO. Local pickup preferred but I can work out a shipping deal with the buyer as long as the buyer pays for shipping and covers PayPal fees.