You could cut the costs down by doing the stripping out yourself. You have a choice of engine out or gearbox out, personally I went for gearbox, as we could slide it back out the way without actually removing it.
To do this you need to remove the centre console and gear stick gaters, then drill the rivets out and remove the ring around the hole.
You could even remove the prop(can't remember if you need to??) and drive to the garage in diff lock.
That way youve saved a couple of hours workshop time.
I think £500 seems a bit steep though? The clutch is only about £60 MAX and the job is about 6 hours making the hourly rate about £70 odd quid!! that seems alot to me!