It does seem steep, the part is £35 +VAT each plus a couple of hub nuts, the rest must be labour which for a few bolts seems more than steep. Take off the wheel (4 bolts), remove brake caliper (2), remove brake caliper bracket (2), remove disc (2), remove hub nut (1).
However there are four potential problems,
1) you will need a torque wrench that can handle high loads, needs to be tightened to 266-294 Nm
2) there are three different part numbers for the hub
3) the old hub can be hard to get off though brute force will work in the end
4) the hub nut is recessed, so a slim socket is needed, because of the torques involved its not always easy to get a slim socket of that size, check this out before starting the job.
Finally the job is straight forward, you could buy the parts and get a local garage to fit them for you and keep the labour down that way.
Hope thos helps