the ebay ones are almost always junk. I purchased a 32gb Class 10 Kingston for $89 from newegg.com . It transfers really fast. 12-14mb per second
Little help here, was it 14 Mbps or 14 MBps?
Either way, those speeds are more than fast enough to play a high quality video without interruption (which I would consider to be the bare minimum usability requirement as far as card speed is concerned.)
There isn't really a hard and fast answer. Technically, Blu Ray rips can spike to 54Mbps, but in testing I did with the Xoom I was getting "acceptable" results with bitrates around 1Mbps (onscreen playback, not connected to an external monitor.)
It is only a Class 4 but it would tide you over for $18 instead of $100. Later you can upgrade to 32GB or add an SD card or USB thumb drives. The maximmum memory is Base+32GB+128GB+64GB+64GB or about 300GB.
Be really careful if you are searching eBay to only search for new items from the US. Also check to make sure they have at least 50 good ratings. Here is a search for 32GB microSD Class 10 but the prices really are not much better than newegg, amazon, or buy.com.