CameraDojo have done a review of a cheapo white balance lens cap purchased from an ebay vendor in China, its cost was under US$10 that’s over 10X cheaper than the leading product from Expodisc.

Ebay: White Balance Lens Cap less than US$10

The results are quite amazing, well worth the $10 investment, however there is no comparison done against the Expodisc product, one is promised soon.

I have a cheaper solution, a mate mentioned he had great results with white top of a disposable coffee cup ;)

Check out the the Cheapo White Balance Lens Caps on Ebay 

The CameraDojo review can be found here: White Balancing Lens Cap Review