I don't know what they were quoting you, but I had the Works shock on my K75S rebuilt after a seal blow out and a longer shaft installed about a year and a half ago.
Shaft, seals, bladder and labor was less than $200 if I recall correctly. I think seals and bladder are about $70 or so. Could go back and find the invoice.
Go to their web site and check the price list. They are pretty reasonable.