Yes, on no account fit poly bushes to the radius arms - I heard lots of bad reports on them from others - and mine caused serious death wobble. I can't help you with the how much, ask a few and see... Your next problem will be the quality of the rubber bushes, if you let the garage source them you'll probably end up with cheap s***. So maybe look for a quote which is labour plus parts and source the parts yourself. Radius arm bushes are a special job, and many folks won't have the correct tooling, so someone who knows their way round a RR ideally.