If you wanted one decent white cattleya orchid, my suggestion would be to avoid EBay and simply go visit the website of one of the many reputable vendors who have quality plants--and, equally important, have return policies that guarantee safe delivery of their plants, especially during this time of year. I just visited Hausermann's website (
Welcome to Orchids By Hausermann On-Line Orchid catalog.) and found a number of decently-priced large white cattleya plants. I bought a C. Bob Betts from them last spring and it flowered this past fall; beautiful huge flowers that were fantastically fragrant. Oak Hill probably also has similar products. And to second Al's comment, you want to make sure that you can accommodate a mounted cattleya. Standard catts get pretty large and might not lend themselves well, long term, to being mounted (unless you're lucky enough to live somewhere that allows you to tie it to a tree and forget about it :-). Good luck with your search.
Steve