Or, you can do some arbitrage and combine products from several websites.
http://jellyfishart.com/
This website sells the full product under the name “1 Jelly Kit.” This is in fact the same exact product that is listed at ThinkGeek.
It costs $382 and includes the tank, 1 small moon jellyfish, and a 3 ounce food supply. The three ounce supply doesn’t seem like a lot, but the site says that it is actually enough to feed three jellyfish for three months, and the kit only has 1 jellyfish.
Buying only the tank costs $285
Buying the 1 small moon jelly costs $20 at this site
Buying the 3 ounce food supply costs $30
There, I just saved you $47 without any effort.
The only thing I would be concerned about is some sort of warranty on the jellyfish, as we want to make sure that it is guaranteed to be healthy upon arrival.