As above can i fit one and will i notice any difference and whats the price like?

Sure if you get the right one you can fit it, but from my driving of the octy I think a front and rear arb from the likes of eibach would be a batter move.

what is an arb and can i fit it myself?

i take it anti roll bar. so can i fit it my self and whats the price like

I think somewhere between £100-200 for a pair of eibach Arbs for a non VRS.

The rear ARB I believe is a DIY job, but IIRC the front one required dropping of the subframe so may require somebody to do it for you then a wheel alighnment thingy done.

Also, a rear ARB for a VRS will fit the Elegance but the front is different.

4x4/VRS/Audi S3/Golf R32 front ARB's wont' fit the Elegance. Neuspeed do a front ARB for the non-GTi Golf that will fit, IIRC it is about £275