it is way cheaper to buy the interchangeables than to buy individual sets. and you can get them cheaper than $60 too. for example right now HObby Lobby has all of their needles and knitting supplies at 50% off. should end tomorrow but the sale comes around all the time. the set would cost about $30 right now. I got both my sets (these are all Boye sets i am talking about btw) off ebay for less than $40 shipped.
And you can get the Denise sets for less than $50 all over the place. I have two sets of the Boyes and am getting a set of Denises for Christmas! 