I really don't want to drag you into a full discourse on Hobie's sourcing and product economics, but would you please tell me a little about the Hobie 18 jib?
That one is interesting... Murrays (who is not an authorized Hobie Cat dealer anyway) sent you some kind of "after market" jib that was not "class legal" for the 18? Certainly that jib was not made by Hobie Cat! We make all of our (USA model cats) Hobie Sails in our loft here in Oceanside California. We do not make an after market jib that is not class legal for an 18, nor do we sell one that is at some different price structure. No idea where Murrays came up with that idea. Sounds like they just made a mistake and sent you some sail from another manufacturer that they sell. It disturbs me that they are trying to pass this off as "the same" or from our loft. All of our dacron sails are made from 5.6 oz dacron cloth. You will find that the cheaper after market sails are likely much lighter weight material.
We do sell a "recreational" jib for the 16 that is roller furling.