I replaced the Alex S500 (Specialized version) with Easton EA50's and they were stiffer. They are in the $150-180 range if you are a good price shopper. Performance has Forte's for about $150, which are so similar to the Easton's that they may actually be them.
From Total Cycling, Campy Scirrocco's with Shimano hubs can be had for $225 shipped to the US. They may have Fulcrums as well in the same range.
I didn't do anything with the S500's until I started breaking spokes, and I can say that I was happy with the Eastons, and they felt like an upgrade, whether they made any performance difference is debatable.