This is what I paid last September for one from Stoke audi
1 x RS4 Rear Sway Bar (Part #8E0511409AL) £93.68
2 x RS4 Rear Sway Bar Bushings (Part #8E0511327D) £6.10
2 x Bushing Brackets (Part #8E0511439) £6.86
4 x Bolts for Brackets (Part #N10127707) £3.35
2 x Bolts for ARB links (Part #N10528103) £0.97
2 x Anti Roll Bar Links £52.32
It is well worth it and I wish I have done it sooner. You don't have to change the ARB links but i did at same time.