Well, the interechangeable set for the nickel plated needles on knitpicks is $69.99. If you were to slowly build on the set, the tips are $5.99 to $9.99. To me, I think that the best deal is just to get the set of needles. But that's just me.
They're really great needles, and I would highly recommend giving them a try if you really like metal needles.