Well figure its probly going to cost around $100-$120 for a rebuild,another $40ish for seal kit and probly another $20-$40 for new rubber bumpers. If theres issues with a shaft theres another $100,or anything else internally cost will go up. If they need setup for you and another $40 to the rebuild price.
IMO if you get a set of 450r shocks,you definitely want/need to have them setup for you and your combination,however it would be well worth it in the end. The 450r shocks will far out perform the Works.