Not much of a choice, and I know there not the best quality, but Ive just bought a pair of Mamba L7 seats (black with yellow piping) for £99
Yes, £99 for 2 seats, brand new!!!
http://www.midlandwheels.com/Shop/P-3020-Mamba-L7-Cub-Sport-Seat---Black-Vinyl-/-Yellow-Piping-Pair.html
They only have the yellow piping ones on offer. the rest are 170 odd for the pair, but still cheap!