I noticed that too, fortunately I did buy 3 sets as it was the max to still get $60 shipping. It's not great as in reality 3 sets gives you all the ball rail ties you need to use the first set and a lot of spare parts you can't use.
I'm still delighted, I think you could make some pretty impressive coasters even with 1 kit.
I've been mulling this over for a while. I want to understand the physics first, so I'm going to build some simple drops and climbs, loops, bends, etc. to see what is possible. I'll just use the bare minimum bricks, beams and technics to find out the basics. Also need to work out how to build a chain lift with motor.
Once I've got that I'm thinking about using existing lego models as a basis for coasters. I have got my eyes on my daughter's King's Castle (70404) - thinking about doing the first frop through the portcullis gates. Probably dragon themed. I think you will need to pull the castle apart to some degree, and rebuild it with the features you want for your coaster and just use whatever bricks and accessories you can lay your hands on to complete the effect.
The possibilities are endless, depending on the existing Lego sets you can lay your hands on. Other thoughts i have had;
-TNMT based on the lair
-Batman based on Batcave
-LOTR based on Helps Deep (and what might be possible with the Tower of Orthanc)
-and if you could get your hands on a UCS Deathstar!!