If you look at the mode of shipping, it says "media mail", 2-9 days. Well, by the time you get it, you'll have to cure it all over again and you know it's gong to smell horrible! To ship 50 lbs. of rock from New Jersey would cost ALOT more than $18.79 to get it here in a reasonable amount of time (overnight?).
Also, the seller only has 3 feedback scores and none of them are for live rock so you can't get an indication from others that have bought from this seller whether it's good stuff or not.
My opinion is that if you want to buy on ebay, there are plenty of sellers in the Tampa area selling for around $2.24 a pound and you know you'll get it quick and they have very good feedback and been around for a while.