Funny story! Tom Fords also come in 50ml bottles for $205 - not only in the big 250ml. I believe Purple patchouli is discontinued, so you won't find through the regular distribution channels. Individual stores (like Neiman, Saks etc) may still have old stocks, but you have to call the individual stores to find out. I don't know the merchant you mention, but of course, going outside of the authorized retailers always carries the danger of a fake/adulterated product.
I also wonder whether there's a reasonable substitute. I don't know that frag well, but other BNers may have ideas.