It is recommended that you replace the whole sway bar as it can rust and wear down under the bushes, rendering any new bushes - useless.
That said, if you insist on keeping the old bar, you can replace the bushes with poly ones (or EOM bushes).. You have a few choices here:
Suspension for Alfa 166
They can supply the bar, or just standard bushes or poly's.
I had mine replaced recently, along with new lower wishbones and it was only about 3 or 4 hours labour from memory - at an Alfa specialist.
Expect to pay between 50 - 70% less for OEM and aftermarket parts if you buy from overseas, EB Spares are great, very reliable. However, you can also look at AlfaWorkshop, Autolusso and Alfisti.net for performance bits and pieces.
So if you can be bothered waiting about a week for shipping, it makes sense to get your own parts and get your mechanic to fit.. but $550 is about right (ish), less if you supply yourself.
Are you using a general mechanic or an Alfa specialist?